2.00mm EM reading 1.86mm?

Not sure what cutters you're measuring (3 or 4 flute), or what you're measuring with (calipers or mic), but one point I'll mention is that it is easy to overdo pressure on your measuring tool (ie pushing a caliper too far or tightening a mic too far) and giving a false reading. I have seen people (even in the trade) tighten mic's like g-clamps (not good, because it twists the frame).

If its a 4-flute, slide it until caliper jaws *just* touch, and rotate it until you get the highest reading - this is your actual size.

You say the cutters are from ebay - in which case they may be worn anyway (not knowing how they've been used / treated).

One other point of note: re-ground cutters can sometimes cut slightly oversize.