ok, the only thing I would say I've noticed about Auguste Jean work is that my books say pieces are almost always signed - and I've never seen an unsigned piece that didn't turn out to be Harrach

(or possibly Sevres in the case of Ivo's amethyst vase) . Some of the books show pieces in a similar vein by Clichy and Sevres as well as Leveille. And I guess there may be Auguste Jean pieces in museums that perhaps aren't signed. However, there are so many VERY similar pieces by Harrach that I'd never buy an 'Auguste Jean' piece unless it were signed either with the enamelled mark or the lozenge, because I've seen quite a few sold as Auguste Jean in the past in Auction Houses that I now know are Harrach.
If the vase is beautiful it shouldn't make any difference to the price, however it does. A signed Auguste Jean vase commands a much higher premium in the cases I've seen, than a similar piece from Harrach. But that's just my personal view, perhaps others will have seen it differently.
Le Genie Verrier de l'Europe, Cappa, shows a number of vases all signed in some way and one vase that is unsigned as Auguste Jean - I'm not sure about the unsigned one. I think it could also be Harrach.
m