I am new to the purse forum, but I noticed that this is actually a problem of many threads in this forum, esp. threads that could otherwise be used as reference threads.
I have a short update regarding my vintage purse that could not be authenticated here in the forum. I sent a mail to Christie's, and got an answer after spectacular 8 minutes.

They will send the information to their specialist and i will have to wait 6 to 8 weeks. If I understood it correctly, Christie will not authenticate, but they will put an estimate of the value of the bag (only in case if it is somewhat valuable).
I also followed the other link that was posted here of an authentication service, they do in general not authenticate vintage bags.
Third, I bought the book "Making of Gucci" which was on sale at
amazon.uk. Although it is a really nice, and I simply love it, I find it not super helpful for putting dates etc. to vintage Gucci. Nevertheless, it is a very recommendable book, very nicely made with lots of interesting pictures.
Maybe this information helps somebody.
And I would love to see really old Gucci purses, from the beginning.