Of course the repertoire of ornaments varies - that was my point. If it was always the same you wouldn't need all those footnote-heavy transcriptions saying how the singer varied their twiddles.

The difference between folk and art music is that on the whole art music created codified lists of ornaments in use (see any number of Baroque instruction manuals) and folk music cultures kept their system more individualized and informal. But there isn't necessarily any difference in how predictable or otherwise they are at any moment.