I'm a bit confused as well.

I did have the lami on L4/L5 in 2002. Which it has been. Now it's being called L5/S1. What I was told by the NS is that no matter what it's being called, the prior surgery and new problems are the same area. It's a natural progression. It just depends on who's reading the films and how they count the vertebrae. All surrounding discs are healthy. It all stems from this "transitional segment".