your description of the surface of this biscuit barrel does strongly suggest an 'overshot' decoration - shame the lid is missing.
I hate to be a pessimist but - and again my opinion is influenced by the fact that I can't see detail of the decoration on this blue vase in close up - is there a possibility that the surface decoration of birds etc., is simply thick enamel painting?? - or is the decoration composed on tiny glass fragments/beads?
Decoration using bright colours applied in the form of enamel paining was a very common feature at the end of the C19/beginning C20, on glass.
If you have a lens/loupe, this should confirm one way or the other.
As mentioned, the very early art nouveau coralene pieces were decorated with images formed in the shape of pieces of coral - whites, pinks and reds.
Two hundred and fifty pieces - all without a backstamp or makers mark of any kind, must be some sort of record - it does make for a difficult life when it comes time for attribution

Art nouveau (Stile Liberty) glass (last quarter of C19 and a tad beyond) not my area, though I can appreciate the beauty of all those Baccarat, Daum, peach blows, Tiffany lamps and iridescent peacock feathers. I might be able to help if you have a drinking glass though

Look forward to seeing more of your glass collection.