Leather Cuirass Lorica Musculata, I used to think no way but

[Dan Howard]

We know from a royal English tomb and effigy that maille was combined with plate armor from head to toe. So, doubling of armor is a real possibility.

No we don't. It is impossible to tell from effigies whether mail was worn underneath the plate or whether mail was just used as voiders to cover gaps. There are inventories that list mail gussets/voiders dating to the beginning of the period when plate began to supplant mail.