So, I've been thinking about this for a while. Correct me if I'm wrong, but didn't the Enclave know about the FEV in Mariposa military base before actually going in and using it? If that's the case, would it be possible that they moved some of the FEV from Mariposa to 87 as a backup plan? I think that would make sense, given they regroup at Raven Rock, making it logical that they knew about the contents of Vault 87. Hahaha, is this something that's already been established? I guess I'm just trying to work it all out in my head. I think it would make sense that the US government had some of the FEV moved there, which was experimented on and later developed into the distinct Vault 87 strain.