Single Operator Multiple PLMNs PM Counters Collection

Hi! I was wondering if anybody knows, how Performance Management (PM) counters are being collected in case of multiple PLMNs being sent from one cell?

The case is that a cell sends 2 PLMNs (NCC is same, MNCs are different). When looking at PM counters, I can see that there HO attempts from another cell towards a cell with multiple PLMNs. There are few HO towards each of PLMNs.

I am trying to understand why would an operator keep two different MNCs in the system? Why not to use just one of them? Also, should I sum all those separate HO attempts towards a cell with multiple PLMNs to get the total number of HOs towards it? I am pretty sure there are counters that cannot be just easily summed together, what to do in such cases?