Blazer rear seat mounts

[Coatingguy]

I'm not sure if anyones talked about this before or not, My question is, I have several rear Blazer Jimmy seats, all 1969-1972.
Some have 2 rear mounts that bolt to the floor, some have 4. The seats that have 2 mounts are only drilled and tapped for the two outer mounts. Whats that all about? Why would one seat have 2 mounts and another 4?

Just so theres no confusion, all seats have the two front mounts that are all the same. No confusion there.