Is there a record tab on a VHS tape?

I have a couple of VHS tapes which were recorded by commercial firms, one about Cholesterol from a drug company, and the other about Macintosh computers sent to me by Apple about 7 years ago. They are each about 25 minutes long, just the right length to copy some footage I shot with my camcorder. The problem is that I can't copy from my camcorder onto these tapes via my VCR. I can do so on other tapes but not on these two. Is there a record tab somewhere on the VHS cassette that should be moved or covered over to allow me to record onto it?