So many experiments has been used nowadays that preference should be made to use this term only when the the reinvention of the folk style itself by original inspiration occurs. Simply said a combination of Folk and Rock, but the traditional tunes in Folk are respected. Folk Music with some electric instruments. This genre wanted to grip the unique moments in such way. Some timide and technically not so well crafted musicians could use this medium as an excuse too.
Last category is seperated.
It's not easy to trace dates of origin of traditional tunes. When the subcategories are used some reinvention thinking the content once more over is still possible. Several of these genres did receive very mch attention in traditional press, not because of their originality, but because of their keeping itself between its own limitations, like the state would prefer to see people like that. The old reference is mostly end sixties and seventies when all the original sub genres from folk were invented and spontanuous. Neo- is more often used when it is referring to those days and instrumental qualities.