Regarding民謡 / Min'yo
I seem that western users confuse 演歌 with 民謡.
演歌 and 民謡 songs are similar in appearance because the singer wears kimono,
but the singing is completely different.
民謡 are not 演歌, but 民謡 singer sometimes challenge 演歌 singer.
However, an 演歌 singer cannot become a 民謡 singer by singing a 民謡 song.
Because 民謡 singers are folk performing arts that require advanced skills.

I made Min'yo' guidance for you.It may be difficult for you.
But these are the sense that Japanese people share for Min'yo / Minyou.
In fact, Japanese can easily judge it from singer, song titles, credits.
I hope this will be useful for your working on the date base.

Min'yo / Minyou is generic name of Japanese old trad song.
Since Min'yo is Japanese original music that continues from
ancient times to the present, it does not have a Western scale
and Western instruments are not used.
The Western scale is seven scales. However, the Japanese scale is five scales.
The Japanese scale "ヨナ抜き" (Yona-nuki : "Yo" means 4, "Na" means 7,
"Nuki" means Without) It without using 4 "Fa" and 7 "Si".
Also other Japanese scale "ニロ抜き"  (Niro-nuki : "Ni" means 2, "Ro" means 6,
"Nuki" means Without) It without using 2 "Re" and 6 "La".
The vocal does not have Kobushi (Enka vibrato).
You can judge Min'yo from this sound.
Or in many cases 民謡 is printed on cover and label so you can judge Min'yo.
民謡 is old trad song from all over Japan.
The area name is printed next to "民謡" credit.

These are the types of Minyou.
追分 Oiwake means the branch point of the Japanese country road.
It is a traditional song that was sung in that area.
As a musical characteristic of 追分 Oiwake,
Rhythm does not have a clear meter (You can not hit a crap hand well)
Wide range (there are many songs from high voice to low voice)
Extend the vowel (one-tone and multiple-voice type, often one character of lyrics etc.
is extended for a long time like a Melisma)

甚句 Zinku (都々逸 Dodoitsu)
It is estimated that it occurred during the Edo period.
It is characterized by lyrics constituting 1 chorus
with 7, 7, 7 and 5 (都々逸 Dodoitsu).
Various lyrics were invented. 5, 7, 7, 5 in some cases.
Many folk songs throughout the country have this form.
There are both a melisma type and a syllable type.
A shout is inserted, which is often inserted before and after lyrics.

シマ唄 Shima-uta is Min'y? from 鹿児島県奄美群島 (Amami Islands)
which 沖縄 Okinawa and 鹿児島 Kagoshima people' trad song.

労働歌 Roudouka = Work song

馬子唄 Mago-Uta is a song for a person to sing while leading a horse.
It also called 馬追い歌 (Umaoi-Uta)、馬喰節 (Bakurou-Bushi).
Many lyrics are in Zinku style (1 chorus with 7, 7, 7 and 5)
It is difficult because it has melisma style and does not have a constant rhythm.
Likewise, cow songs fall into this category.

舟歌 Funa-Uta is Sailor's song. It’s kind of Work song.

木遣唄 Kiyari-Uta is song for carrying heavy logs,
workmen's chant while pulling a heavy load.

地突唄 Zitsuki-Uta, According to Japanese trad music classification,
it is one of work songs. It's the workers singing with shout
when hardening the construction site before building the house.
We will hang a weight of about 112.5 kilograms by assembling a large wooden scaffold.
16 to 30 people with rope attached to this are pulled up rhythmically
when singing it with shout. This will facilitate integration of work.

ユンタ Yunta is is a form of trad song transmitted to the Yaeyama Islands
in Okinawa Prefecture, which is a work song in which men and women sing alternately.

Also 舞踊 = Buyou, It belong under the Min'yo.
舞踊 = Buyou is old trad dance song with Japanese instruments Shamisen etc.
In many cases舞踊is printed on cover and label so you can judge舞踊.

盆踊りの歌 Bon-Odori song,
Bon Odori meaning simply Bon dance, is a style of dancing performed during Obon.
Originally a Nenbutsu folk dance to welcome the spirits of the dead,
the style of celebration varies in many aspects from region to region.
Each region has a local dance, as well as different music.
The music can be songs specifically pertinent to the spiritual message of Obon,
or local min'yo folk songs. Consequently, the Bon dance will look
and sound different from region to region.

音頭 Ondo,
An "Ondo," usually refers to a kind of song with a distinct swung 2/2 rhythm.
This "swing" can be referred to as "Ukare" in Japanese.
"Ondo" is a term used in older Japanese genres,
but it is still used today when referring to songs written in this swinging style.
Sometimes the rhythm is NOT swung and it is played straight through. This is called "Kizami"
There are other names used to describe older Japanese genres of music.
For example, "Fushi" or "Bushi" (節), with its literal meaning of "node," "knuckle,"
or "joint," refers to the nodes found in bamboo, usually found at a steady sequence.
Thus "Fushi" can also have the abstract idea of "sequence" to refer to notes
and beats in a sequence, i.e., a melody.

Not every old Japanese melody with a swung rhythm is called an "Ondo,"
as sometimes the term "Fushi" or "Bushi" is used to refer to a tune
with a swung 2/2 rhythm, both of these having more or less the same meaning
of "tune" or "melody." The folk song Goshu Ondo,
for example, does not follow this rule, as the rhythm is NOT played in a swung fashion.
The folk song Tankou Bushi has a swung 2/2 rhythm,
even though it has "bushi" in its name.

In Japanese folk music, "Fushi" and "Ondo" follow the name of the song.
For example, Tokyo Ondo, Mamurogawa Ondo,
and Hanagasa Ondo all have "Ondo" in their names.
Kushimoto fushi, Burabura Bushi, and Soran Bushi all have a rendering
of "Bushi" or "Fushi" in their names.

Part of the Japanese Obon celebration involves participating in the local community dance.
The tradition of the Bon dance, or Bon odori (盆踊り), dates back a few hundred years,
and it is usually accompanied by the local tune.
In recent times, new music has been used for Bon dance accompaniment,
including late enka hits and music written specifically for bon dancing.
The "Ondo" rhythm has always been common in Japanese folk music,
but even the newer music written for Bon dances has been written in this style.

It is common to find names of newer music with the word "Ondo" attached to it.
For example, Japanese franchises such as anime, video games and
Tokusatsu TV series have their own ondo: the Pokemon Ondo, the Naruto Ondo,
the Hunter x Hunter Ondo, the Doraemon Ondo, Ojamajo Doremi Ondo,
Shiawase Kyoryu Ondo, the Love Live! Sunshine!! Sunshine Pikkapika Ondo
and even the Super Sentai series has several Ondo songs such as Carranger Ondo,
Bomb Dancing Megaranger, Hurricane Ondo, Bakuryu Kazoeuta, Let's Go On-do,
Minna Summer DAY Ondo, Kyutama Ondo.

There is fan-made Touhou Ondo and DoDonPachi Ondo.
Ondo were commonly used as the opening themes for anime in the 1960s and 70s,
especially with Tatsunoko Productions.
Even non-ondo music is starting to make the bon dance scene.
The selection ranges from traditional sounding Enka,
such as Hikawa Kiyoshi's "Zundoko-bushi," to more modern non-Japanese hits,
such as the Beach Boys' "Kokomo."

騒ぎ唄 Sawagi-Uta.
Geisha sing to play with customers. Tempo is fast, lively and bright sound.
Geisha sang this to warm banquet up with shamisen and Japanese drum.

今様 Imayou / Imayo
A style of Japanese old songs. 今様 Imayou / Imayo means "Modern and Contemporary"
and it was the name meaning "Modern epidemic song" at the time.
In the Heian period (794 - 1185)
今様 Imayou / Imayo occurred in the middle of the Heian period.
In the latter half of the Heian period, it was left in the record of the history book
that 後白河天皇 (Emperor Go-Shirakawa) loved it, he was too passionate and
had sore throat for 今様 Imayou / Imayo.
The lyrics are characterized by 7, 5, 7, 5, 7, 5, 7 and 5 constituting one chorus,
and various lyrics were produced. Songs are syllables and melisma types

Geisha sings old Japanese songs in response to customer requests.
That is not necessarily only Minyou.
Geisha was singing 歌謡曲 Kayoukyoku,長唄 Naga-Uta,清元 Kiyomoto / Kiyomoto-bush,i
民謡 Minyou,端唄 Ha-Uta,小唄 Kouta,宮薗節 Miyazono-bushi / 薗八節 Sonohachi-bushi.
If 三味線 Shamisen is used, these kinds are often collectively called Minyou.