So I noticed that the current preferred seed for doing 1.3.12 runs is 453918283, which after the first corner room, has the SCP-970 corridor then the corridor with those 4 SCPs etc.

But when I put this exact same seed, the map is different! I first encounter the 4 SCPs, then a corridor with an elevator, then SCP-970, and then when I see it the map is completely different, just with a somewhat resemblance.

Why does this happen? I'm on the exact same version as the latest run.

1.3.12 has two different seeding options. Try change "Use numeric seeds" in options - Advanced tab, that should help

Use numeric seeds