And if Rainer Barbi made a replacement stem for one of his own pipes how would you know?
This gets into interesting territory. With book collecting, reputable dealers will note when a book has a “supplied” dust jacket, meaning the original jacket for the book was not present and one from another book was married to the book in question; this jacket could very well be correct in every detail and perhaps even be from the same print run, but is something that should be noted in the description of the book. Sometimes there will be wear to the binding of the book that does not have corresponding wear on the supplied jacket, which can give a clue that the jacket is not original to that particular book. Years ago, I bought a Ross Macdonald book from a dealer. When I received it, I noticed that the dust jacket didn’t have dampstaining (water damage) like the book’s binding did. I contacted the seller immediately and asked if he had the jacket with the damage—the book was inscribed to a friend of the author, and I wanted the jacket that belonged to that copy and person. I suspect the dealer thought he was doing me a favour by putting the better jacket on the book, but I wanted the one that belonged to the recipient and was much happier when I was able to put the lesser condition jacket on the book it belonged on.
When it comes to books signed by authors I collect, I prefer period correct signatures contemporary to the books whenever possible. Because I’m familiar with the handwriting of the writers whose work I collect seriously, I usually have a relatively good idea about what period the signature is from, but that’s probably unusual. With pipes, you really have to rely on the seller being honest and forthcoming with the pipe’s history.
With regard to a replacement stem for a pipe missing its original one, I guess it’s better to have one replaced by the artisan who made the pipe rather than some third party version, although it seems possible that a George Dibos might make a better stem. I guess it all matters if your priority is functionality over history or lineage.