Keep drawing revisions out of the wrong conversation
Most revision confusion is a filename problem wearing a technical disguise. Two rules and a habit will remove nearly all of it.
Someone attaches a drawing. Three weeks later a different drawing with the same name is attached by someone else. Both are in the thread, both are called valve-spec.pdf, and the question of which one the quotation was built against now takes an afternoon to answer.
This is not a technical problem and it will not be solved by discussing the drawing. It is a naming and quoting problem, and it responds to two rules.
Two rules
Rule one: the revision goes in the filename, and the filename never changes meaning. A file called frame-bracket-revC.pdf is always that revision of that document. If revision D arrives, it arrives as frame-bracket-revD.pdf. Nothing is ever overwritten in place and nothing is ever called final.
Rule two: when you refer to a document in a message, name the file and the revision in the sentence. Not "as per the drawing" but "as per frame-bracket-revC.pdf, dimension B". The sentence then stays true when it is forwarded, quoted or read a year later.
The five failures this prevents
Date is not a revision - Two people can export the same drawing on different days. A date tells you when a file was made, not which version of the content it holds.
Final is not a revision - final, final2 and really-final are the classic sequence. Use a letter or a number and keep going.
The revision belongs to the document, not the email - Do not rely on "the one I sent on Tuesday". Threads get split and forwarded.
Say what changed - One line with the new revision - "revD: outlet designation corrected" - prevents the recipient re-reading the whole document to find out.
Withdraw explicitly - If a revision was wrong, say so in the thread by name. A superseded file that is never withdrawn stays in circulation.
The habit
The habit that makes the rules stick: before you send any message that will change what somebody builds or quotes, re-read it and check that every document you mentioned is named with its revision. It takes ten seconds and it is the only part of this that requires discipline.
Name the file and revision in the message as well as attaching it, and tell us which revision the enquiry is built on.