Of course you are right there is no certainty its a Harrach blank
The colour change is quite distinctive, and Harrach like, but as you said it could be a function of the size (and age actually). I've had other signed Moser bits that small that showed a normal Moser graduation -but being signed they were probably a few years later.
We can't even be sure it's a Moser label, with what it says they might just have assumed it was theirs.
We have to work with the balance of probabilities, and you quite right to pull me up and correct that.
but, for me at least, the sense of discovery is still great fun.