It's not critical they are both perfect (at least not in my experience), differences of 5mm or so I can't feel on the track. So long as none of them get to the point of hydraulic lock on full compression you're fine
Things like the condition of the shock seals or the coating on the shock shaft can make a big difference to how far/fast the shock rebounds, so unless you have new seals and shafts every time you refill the shock don't worry too much if they are slightly different.