nesdev.org

The wiki says that NROM (Mapper 0) cartridges have 1 or 2 16KB PRG ROMs and 1 8KB CHR ROM.
But by watching into the iNES header of my collection of NES ROMs, I see that many mapper 0 ROMs actually have up to 7 of each.

Is this right?
is there some bank switching going on for mapper 0?
if so, how?

You're probably misinterpreting the header. Check the sizes of the files; they should be between 24 (16+8) to 40 (32+8) KB. If they are, you're misreading the header. If not, they're not NROM ROMs.

Oh yes, you're right. Upon closer inspection, all these games are the ones known as sachen
Their headers report having mapper 0, 7 PRG ROMs and no CHR ROM.
Thanks!