Douglas,
These models simply don’t correspond to any yacht guns that I’ve ever seen, especially in regards to the carriages. I’m also inclined to agree with John, that they were originally intended to be display models.
The marked initials and years probably do have a real significance, but I wouldn’t make a big bet that they record the dates of manufacture.
I believe that Allen offers a valid speculation, those dates might even represent GAR charters.
I don’t think these models are irrelevant, to the contrary, I wish they were mine.