Based on what I've read here they could:

1) Have EPROMs that are currently erased/corrupted
2) Not be bootable in a standard NES/Famicom
3) Not have data burned to the EPROMs (if it indeed has them) that is bootable data (additional storage?)
4) In need of repair as suggested by the sticker

Since it looks like the cart snaps closed, your only bet would be to X-Ray the thing but good luck convincing your local dentist to let you use his expensive machine and film to check out what is inside the cart.

If these are indeed some sort of intermediary for writing data onto a FDS disk then the data could be modified in such a way that it requires the FDS to boot it. I don't think you can write the data dumped from a FDS disk onto an EPROM and wire it into a reproduction cart with it just booting. Pretty sure it has to be hacked somehow.