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!

If there’s two bishop pawns that can be moved, they will be referred to as “KBP” and “QBP”, respectively. For your first example, 3... f5 would be written as 3... P-KB4. Hope this clears things up.

@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?

The N on c6 is preventing 3...c5 or 3...P-QB4, so "3...P-B4" is not ambiguous.

@Rocky64 Gotcha. Thank you very much!

Rocky64 έγραψε:

The N on c6 is preventing 3...c5 or 3...P-QB4, so "3...P-B4" is not ambiguous.

It is OK (3...f5), but there are errors in other parts of it- e.g. it's more or less obvious that 5...P-Q5 should read as 5...P-B5.

http://www.chessgames.com/perl/chessgame?gid=1292862

It sucks that we have many excellent old books for chess but which happened to have been printed at the time when descriptive notation was still being done while the rest of the world evolved to algebraic. It can be read by learning what means what, its just such so inconvenient.