Question about Descriptive Notations


@hitthepin It does. Much appreciated! The attached photo is what I was looking at when this question came to me, out of the book "Paul Morphy: The Pride and Sorrow of Chess." It would be safe to say then, I assume, that this is atypical, or maybe incorrectly written by the author?
In descriptive notations, how was one to distinguish the specific pawn being moved when noting a bishop's pawn move on the kingside versus the queenside?
Looking over a match between Morphy and Rousseau, what would today be recorded as 3...f5 is descriptively written as: P-B4. I understand it's describing the pawn move located in front of the bishop...but how would one know which bishop? This question came to mind when I then read that on move 9...c6, which is written as: P-B3. In this specific situation, it's clear that it's referring to the pawn in front of the remaining bishop, but suppose move three was P-B3 and the second bishop-pawn move was B4, how would one know whether it meant a second move of the bishop-pawn, or a move of the yet unmoved bishop-pawn? Or better yet, with the first bishop-pawn move, how does one know which of the two possible pawns it is referring to if trying to recreate the match on a board?
I'm certain this is a silly question but, all the more reason why I would like to understand...so I at least have a grasp of the silly things I don't currently.
Thank you!