At the time your Parker Bros. VH-Grade was made, the heaviest 12-gauge loads the North American ammunition companies offered were 3 1/2 drams of bulk smokeless powder pushing 1 1/4 ounces of shot or 28-grains of dense smokeless powder such as Ballistite or Infallible pushing the same 1 1/4 ounces of shot.
The North American ammunition companies held their smokeless powder loads offered in the 2 5/8 inch 12-gauge shells lower than those offered in the 2 3/4 inch and longer shells. Same thing holds for the 2 9/16 inch 16-gauge shells and the 2 ½ inch 20-gauge shells. The very heaviest 2 5/8 inch 12-gauge shells I find offered were 3 1/4 drams of bulk smokeless powder or 26 grains of dense smokeless powders such as Ballistite or Infallible with 1 1/4 ounces of shot. These heaviest 2 3/4 inch loads were very high pressure according to a DuPont Smokeless Shotgun Powders (1933) book I have. It shows the 3 1/2 drams of DuPont bulk smokeless powder pushing 1 1/4 ounces of shot as being 11,700 pounds; 3 1/2 drams of Schultze bulk smokeless powders pushing 1 1/4 ounces of shot being 11,800 pounds and the 28-grains of Ballistite pushing the 1 1/4 ounces of shot being 12,600 pounds!!! There were plenty of lighter loads being offered, but American shotgunners being what they are, I'm sure many were opting for the heaviest loads available.
So, your gun very likely digested some very stout loads back when its metal and wood were a lot younger. No one can, or should, tell you over the internet what ammunition may or may not be "safe" in a given gun. That takes a qualified smith with the gun in hand. People can tell you what they use in their 1903 vintage Parker.
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