I think, to actually be a “Boiler Maker”, the shot has to be in the beer. I’ve even heard ot said that instead of pouring it in that you just drop to the shot, glass and all, into the beer.
I was never a fan of beer so I have no practical experience. However, I have seen my stepdad, the dear Ralph Ernest Wall, formerly of the Merchant Marine, God Rest His Soul, pour his shot into his beer at a bar in Arnold, PA and also at the old Elks Club in New Kensington, PA. that was circa the 1960s.
At one office party I gave Patricia Carole Smith, formerly of Winston-Salem, a bottle of creme de menthe and when she opened it, it sort of popped. When I got home I had little green dots all over my face. She said that she looked that way when she woke up the morning after.
I always suspected Mr. Green Jeans was kind of odd!