Fox Collectors

I have an A grade 20ga that letters to 1916. I checked the chamber length with my chamber gauge they measure 2-3/4". Can I assume that they were lengthened at some point? The previous owner said they were never lengthened when he owned it, but of course he doesn't know what could have been done to it before then. Nothing on the card either. Doesn't really matter to me; just curious if it could have come from the factory that way?

Can I assume that they were lengthened at some point?

Short answer is yes.

If it came from the factory intended for 2 3/4-inch shells the chamber would be 2 5/8-inch. I have an AE-Grade 20-gauge from 1920 that was ordered for 2 3/4-inch shells and it has 2 5/8-inch chambers.
From the 1890s to the introduction of progressive burning smokeless powder, high velocity, 20-gauge loads in 1922, the heaviest 20-gauge loads offered in the "standard" 2 1/2-inch shell was 2 1/4 drams of bulk smokeless powder or 18-grains of dense smokeless powder (such as Infallible or Ballistite) pushing 7/8-ounce of shot.
In the 2 3/4-inch or longer 20-gauge shells, our North American ammunition companies offered a bit hotter load of 2 1/2 drams of bulk smokeless powder or 20-grains of dense smokeless powder (such as Infallible or Ballistite) pushing 7/8-ounce of shot --
but really the advantage of those longer shells was more/better wadding.