Someone just gave me a load of VHS tapes

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When using a VCR to record TV shows (not for archival purposes but to re-watch for later), how many times can the tape be re-used before it should be thrown away?

I usually use standard grade VHS tapes for just re-watching show's for later. I would use the tape from start to finish at SLP speed and I always start off the cassette where I last left off (to insure the whole tape was used). Once the tape reaches the end I would rewind the tape back and record over what I've already watched. I've always thrown the tape out after the 8th rewind, I thought if I go beyond that number I risked damaging the VCR with a worned out tape...