As far as I researched no. He created his own pieces as far as I know from what I have read. And some do not have enamelling on them.
And from what I have seen in museums in France.
'Both in it's classical form and in its novel plasticity, which Jean effected with pincers while the metal was hot, the piece anticipates it's creator's future works'. Source - The Art of French Glass, Janine Bloch-Dermant page 27
I have observed one difference between his signed pieces and the Harrach pieces, (apart from the instinctive 'it just doesn't look right' ). I'm not ready to divulge that but it is something I am observing when I see pieces that come up for sale that are not signed v those that are.
All I can say is that I would not buy an Auguste Jean vase unless it either was signed or had the glass pastille mark on it.
But that is me.
However, to counterbalance that I have read in one source that 'Usually they are signed' - and also seen a piece in another French book that is apparently identified in that book as an Auguste Jean piece but is unsigned. However in the case of the latter book, there are numerous inaccuracies in identifications throughout the book which rather means that it puts doubt on other pieces in the book especially if there is no signature or definitive provenance.
None of which is conclusive evidence that Auguste Jean created unsigned pieces.
And none of which is conclusive evidence yet, that means he didn't.
I'm just not willing to take the chance when large sums of money are involved, and what you really want is an Auguste Jean vase not a Harrach/other maker vase.
Funnily enough, even taking into account that all his vases were individual, whenever one comes up that isn't signed, it never seems possible to exactly match an element of the unsigned piece to an element of any of those around that are signed. Or at least I haven't been able to so far, and no one else seems to have been able to do so from what I have read so far. That's not to say this is conclusive evidence that .... (see comments above).
I do think it might be possible in future to accurately identify those that are Auguste Jean (if there are any unsigned) and those that are not. There are elements that differ to the eye. And it might be possible to test the glass of each and see if there are differences in the make up of the glass itself between those made by him (or at least in France) and those made in Bohemia.
Obviously happy to eat my hat if my surmising all turns out to be incorrect - which is eminently possible.
m