Note that from 1875-1887 "IF" the gun were cylinder bored it would not have the Not For Ball mark nor the muzzle gauge mark so would have been essentially identical to the 1868 mark.
The first mark to the left from 1868 through 1925, intertwined VGP from London or VBP from Birmingham was used on guns which by request of the maker were submitted only to Definitive proof. The heavier Provisional proof load was used with the gun in the finished state ready for Definitive proof.
My old Clabrough built W Richards side-lever hammer gun carries this mark. It is cylinder bored in both barrels so has none of the choke related marks, could have been built anywhere from 1868 to 1887, but I don't believe Clabrough dates back to '68.
