Read the instructions in front of the packet. If you don't have that download policy letter 11-07 fron the nmc. I don't have it with me but I think the tonnage does not matter but the officer signing it must have the endorsement. Also I think some of them be completed in a simulator or at least that is my take on it since I too work on tugs.
I have read the policy letter and you are correct it does not state a tonnage limitation. Ship underway at sea is the only specification I have found. I was anticipating some stories of NMC denials, the fact that there have been no such comments is a positive thing for me.