Interesting observations, and I'm glad you've expanded on that - I didn't like to say anything on first looking at the cover pic of item 185, but as soon as I saw that vase, my instinct was it is from the same 'stable'/'region' as those on this thread.
I agree, the age of the items is up for debate and it could transpire that some could be older than others. I've also thought it could also be possible that these are all old, and that on the ones where the gilt has worn off cleanly they just look a lot brighter/cleaner than those that still have their gilding. But yes, definitely up for debate.
I found something else today. A blue opaline decanter with a tall spire type stopper. These type of items look quite 'Persian' and are often sold in pairs, some transparent red etc, all enamelled. I can see that the 'pattern' of decoration is different to those on this thread, but looking close up, the swirls, curls, all over etc, .... not much different in 'style' to these. And some of the pattern has similarities with the Beykoz vases as well to my eye.http://www.ebay.co.uk/itm/Magnificent-large-Bohemian-Opaline-hand-cut-glass-decanter-/201020189656?hash=item2ecdbcabd8&nma=true&si=l2MBzUYPY0OGjxE48GmpcUBq724%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557
I've still not got a clue where these decanters hail from though, although the many I've seen are sold as Bohemian.
So perhaps it's possible the one that Cathy posted that has the 'feathers' plume mark on it, maybe the crucial catalyst?
With regards the ones that just have a letter plus some numbers marked in black on them - I honestly don't know if that is a Harrach 'marker' or not.
The reason I say that is I've found a Richardson's vase, marked Richardson, but also marked with a P then three digits. The P is written in the same way as the 'P' found on many Bohemian vases (thinking of the PK ones just as one example), with a little dash on the bottom of the upright stroke and the horizontal strokes of the curve sticking out over the edge of the horizontal. Obviously I know that with other 'clues' as well as the numbering on the base, items can be properly identified, but I think it just shows that if the Richardson mark had worn off, and the number and letter P just left, it's possible that vase might have been attributed as Bohemian because of the way the mark has been enamelled.