Ouija board, QuelleFromage - thank you ever so much for your input.
You are both right, I think … I am seriously considering leaving the handles for later, and maybe even let the money go towards a Picotin MM (I would be close to halfway there). On the other hand, maybe it is wiser to invest in the bag that I already have and let Hermès do their best with it. I guess there may be problems that only a trained eye could see, but in such cases I wish the quotes would give the reason why a measure is recommended. I don’t suppose Hermès will be too happy about follow-up questions?
And yes, that was quite a scary SA ... She also took it for Togo, and claimed that the measurements and dustbag were all wrong, too. I guess she must have been new on the job, but still. In the end, though, a more senior SA stepped in to say that she didn’t see anything immediately wrong with the bag.
I am well aware of the slouchy-Birkin thread, and certainly will introduce mine to its peers as soon as it gets back!