Peter, good notes! However going back through research , Andrew Mowbrays "The American Eagle Pommel Sword" (1988) and the 'unthinkable', using the search here
I found some interesting things.
In a brisk discussion between Bryce and Glen(2018), two of the local specialists here IMO of British and American swords, they revealed some most intriguing details, well supported by their in depth research:
ALL Osborn blades have G or GG, with no determination as to why these letter 'G' are singular or paired. Suggestions are made that perhaps the GG came after Osborn partnered with Gunby in 1808, nothing substantiates this . These letters seem to occur on officers sword blades, but not as far as seen on the troopers sword blades. As these are typically at the very highest part of the ricasso, so not easy to see with the langets typically on troopers hilts.
Osborn seems to have ended the convention between 1810-1816.
GILL: This is most disturbing, as Mowbray (1988, p.97, c.1805) states the 'G' was the house mark for Gill? All indicators at this point claim, as noted, NO Gill blades have a G.
There are notes that early, that O over a G occurs on an 1808 blade (Osborn&Gunby? Mowbray. p.112)while an 1805 blade (p.105 Mowbray) has a deep 'O';
On p.104,p.102 either O or Ob thought Osborn.
None of the other makers/cutlers (Gill and Osborn produced blades while others were typically cutlers) had these letters on blades, yet all were exporting swords to America.
One blade in this period has the number 12 in the same blade location.
On some occasions it seems I have seen a '3' on Gill blades.
So what we have here seems to be some sort of administrative system in blades being produced and exported to America with these makers. There was a notable commerce in these swords between England and America in the period 1794-1830s. It is important to remember that American colonists were still basically British culturally after the Revolution into early 19th c.and American industry and commerce was not yet well developed in many cases.
So British swords and blades were notably exported to America by Gill, Osborn, and a number of other makers at least until 1820s.
Interesting note on the term cutlass, and while pretty much everywhere the terms hanger and cutlass seem to have been interchanged almost invariably, aside from the Spanish....who had the term machete interpolated in the same capacity. Seems odd the British resisted the cutlass term so late and all sorts of speculation might be added here.
Gill is the only maker who used 'WARRANTED NEVER TO FAIL' on his blades, but others followed suit but more briefly with 'WARRANTED' alone.
Not sure on the changing of blades note, but it seems the reuse of blades and swords held in stores or rendered obsolete by changing patterns was well established. The M1796 saber was so ubiquitous that by the time it was superceded by the M1821 (1829) these ended up everywhere, America, India, Germany produced their own version the M1811 Blucher etc.
The 1821/1829 heavy cavalry saber when replaced by 1853 were in Tower stores and made into practice swords, even attempt to make cutlasses.
same was done with numbers of M1796 heavy cavalry in Tower, attempt to make into cutlasses but most of these destroyed in fire there.
Getting back to the original subject, this Gill blade on an unusually earlier style hilt, it is not unusual to see earlier hilts with later blades. In Wallace Collection (Mann, 1962) there are many later blades mounted on earlier hilts.
All conundrums.