Fox Collectors

I have noticed there is a variation of the recessed pin (slotted and smooth) on the Sterlingworth Pin Guns in a relatively short period when they were available. Why were there two different styles?

It appears to me from the pictures I've saved, and the three that I have, that the early The Sterlingworth Co. guns in the 50xxx serial number range have smooth heads to the pin.
By 50491 we begin seeing frames with the Ansley H. Fox pointed shape of the side-panel. I don't have any pictures of guns in the 51xxx range. By 52190 heads of the pin are slotted --
Of course there are outliers. Serial number 50243 and 50248 have the pointed side panel, slotted heads and 50248 is marked STERLINGWORTH on the sides of the frame!!

In the low 53xxx range they change from The Sterlingworth Co. markings to A.H. Fox Gun Co. markings on the left barrel and just STERLINGWORTH on the sides of the frame.

In the high 589xx serial number range we begin seeing ejector guns and they have smooth heads to the hinge pin.
while the extractor guns continue to have slotted heads.

Thanks for pictures and serial number breakdown. Do we know the reason for different styles? The two most common reasons I have come across for any changes like this is money (cost effectiveness, easier to make) or improvement in the part. Thanks again for the background and dates!!!