This is not a Vlim-specific issue. I don‘t know any serious collector who would consider the gun in the thread you linked to have provenance...... - and the thread I gave a link to the pistol was brought back from WWII. Please let me know why this is "no real provenance" for you? In other words, what would you need to make it a "real provenance" for you?
All there is are the recollections of the thread‘s OP regarding his dad having the pistol when he grew up and telling the standard GI story of having taken it off a German officer. In most cases those are fish stories. But in this case there isn‘t even any evidence supporting the hearsay that this was indeed the gun that Dad brought from Germany.
There is no indication how old the OP in that thread was; there could have been many years post-war before he was born where his father could have bought the surplus Luger; they were cheap back then.
Now if there were a matching bringback paper with the serial and Dad‘s name, THAT would establish some provenance.