Suppose my merit stats show that I haven't sent any merits (even that is only for the last 120 days) but that doesn't mean I am a merit hoarder.
What if I don't really have any merits to send and I have sent it all already?
I might have not received any merits in the last 120 days and so I couldn't send it to others as well.

Obviously, if you haven't received any merits in the last 120 days, I can't expect you to send any. I don't expect the same from newbies either. I am not doing any lengthy checks on each user whose post I want to merit. Like I said, I would just look if you are receiving and sending. In your case, you are doing both. I don't care about the numbers. But let's say your stats look different than what they are now. You have received enough merits to have sMerits to send, but you aren't sending any. 9/10 times I wouldn't merit your post because of that.