Yes, there were some without the bulge.
The P11A at Barber is a beautiful restoration, but not correct in several aspects - mostly minor technical details that only someone with a P11 would see.
Some P11s received the large tank, which didn't have the bulge. Some of the Rangers did not have the bulge, either.
Matchless was bankrupt when the P11 series ran, and Plumstead did whatever it could to fill orders. That beautiful tank on the P11 and N15/G15 came in several different variants - with or without the bulge; with or without the quick-release gas cap; with buttons on the back for the rubber band or with a tab to bolt to the frame; in the slightly under 3 gallon capacity or about 4 gallon capacity; in alloy or steel. This tank design was used on the AMC scramblers from the '50s until the end. The bulge was put on tanks to help better show off the badge. Competition bikes did not need a bulge, as the logo was usually painted on the tank, big enough to see from the stands (Matchless tanks were usually red or black with a big =M= logo in silver, AJS a Robin blue with the stylized AJS logo)
Alloy tanks are really rare - typically only on 'special' customer or factory bikes. My G80CS has the large tank without the bulge, the 3-turn to release cap, and the tab to bolt to the frame. My G15CS has the small tank with the bulge, quick-release cap, and buttons for the rubber band. My Ranger has two small tanks - one with the bulge, one without, both with the buttons and quick-release cap. I currently have the bulge tank on the bike. I honestly think the non-bulge tank is original to the bike. Both bulge and non-bulge have the inserts for the badge screws, not used on the Ranger and just filled in.
