Help ID this 4-hole MV type

[NoisyVia]

Hi,

I've got a couple clips below and i'm wondering which MV type is likely being used in them. When I hear 4-holers with more gain and they don't have their inputs jumpered externally but they have a MV installed in one of the input holes, is that likely an internally jumpered inputs with a pre-PI MV? It doesn't sound to me like an extra preamp stage but maybe you guys know better. What mods would you think these would have?

examples:
https://www.youtube.com/watch?v=R9vEpmmdFmc
https://www.youtube.com/watch?v=dP-mFWMYcBI