Tape Bacup Question

I use DLT-IV tapes on a Compaq DLT8000 drive. I buy 40/80 tapes. I’m on under the impression that 40/80 means 40gb uncompressed, 80 compressed. Is that correct? The reason I ask is because when i checked the details on the tape it says that it wrote 130GB to the tape. I thought it would max out somewhere around 80GB. Is this normal or am i losing my mind? Thanks in advance to anyone that replies.

Wil