First I can see why you would say this a a Peru, it has the V mark/cease above the areoles, spination is similar, etc.
My personal opinion is this plant is a hybrid that has Cuzcoensis and a true Pachanoi (not PC, from my findings I believe PC is a hybrid).
Why this isn't a Peruvianus. Remember this is my opinion/findings on two very closely related species, you may have a different opinion, please share it.
No double central spine, every peruvianus I have seen has double central spines at some point whilst cuzco does not. Cuzco also has a tear drop at the very base of the central spines, this is evident on this plant but hard to see in the pic.
Peruvianus spines tend to be a brown or thorn colour, whilst Cuzco has a pronounced yellow colour especially towards to top.
The body colour confuses me, it is a nice deep green colour with no sign of a blue shimmer as yet. This can can change with environment so will wait and see.
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