John,
The early years of the PC (after they got over the initial "custom" one-at-a-time orientation) saw almost everything going through Lew Horton, followed by some abortive attempts by the Stocking Dealer Program to take some PC models. Some folks talk about the unique and solid relationship between LH and the PC, and I'm sure most of it is true. I've talked to a few folks at LH as well, and one rep told me one time that they didn't have all that much sway as to what was being made, they just got a visit from time to time by folks from the PC showing them the new models they were making, and the inference was "here's what we have coming, how many do you want"? It seems, the proximity of LH to the factory could have had more to do with their exclusivity than anything else (?)
It wasn't until the late 90's that other companies started taking any amount of new PC runs, the first appeared to be RSR with their Light Hunter line, followed by others (Camfour, Bangors, Sports South). It is my belief that many of these other companies got into the fray after the dreaded agreement when nobody could sell Smiths and LH was sitting on loads of product in inventory (in essence, they told the PC to stop loading them up). That's about the time that the Heritage line was starting to take off, just to quickly crash leaving LH to sell off loads of them to CDNN and others at what appears to be a big loss.
Anyway, long answer to a short question, but for many of the early years (~1990 - the late 90's), while LH had much of the PC production, they had fairly little input into what was being designed and made.
As for over-run guns, almost anything goes. We've seen many Wischo guns (their exclusive German distributor) distributed in the US by many other distributors, when it came time to clean out the warehouse the factory didn't care who took the product, just that they sold it off and got paid.