In the absence of documentation (so far), there has been some discussion about the significance of certain marks on Harrach pieces, and what those markings mean. The Harrach "feather plume" mark has been de-conflicted with any connection to Webb by most informed collectors; therefore, we can reliably say that pieces with this mark are undoubtedly Harrach production. In some cases, the feather plume mark can be used as a "missing link" to positively attribute an alpha-numeric marking to Harrach, as in the first example below:
This piece from my collection has a pretty typical Harrach type marking - the top half is a number - 1132. The bottom half is alpha-numeric - K. 248.
From the internet comes this example - same decor, different shape. The marking is quite similar , with one notable exception - the feather plume mark is present. Note that the top half is again a number - 1134/4. The bottom half is the same as the one in my collection - K. 248. This tells us two things - One, that the vase in my collection is indeed Harrach, and Two, that the alpha-numeric portion of the mark refers to the DECOR. The top half of the mark, then, must refer to a shape or variation on a shape.
I have two more examples in my collection which further confirm this:
This first piece I picked up at a show last year:
Then, just a week ago, I picked up this next piece on eBay:
Both have the same alphanumeric marking - P.513. Both also have precisely the same decorative motifs. There is a slight difference in the top number - 1074/5 on the first (smaller) one, and 1074/4 on the second one. I believe these are numbers referencing the shape of the vessels and/or the glass to be used. There is also the addition of a third mark - a number - on a third row at the bottom. My working theory is that this is to signify that this vase is one of a pair, and that somewhere there should be another one with either the exact same mark, or the next number in sequence (i.e. 10 and 11 make a pair, or 21 and 22 make a pair, or 10 and 10 or 21 and 21.
I also have pieces with a "V" in the alphanumeric marking - both with feather plume mark:
Below are two vases with the same decor - they share the decor designation P.474. The glass and shape numbers are different. Also, the one without handles has no gilding over the initial enameling. My theory is that this was done to order.