don't know if the number is correct or not: Ideale model numbers are kind of a black art. I had one (sold it without trying it out) and the cut-away was not exactly as this one (which looks a bit cruder than mine, I think) but it still could be factory work. I just called mine an Ideale "Swallow type" with steel rails, the buyer didn't care about correct numbers...it had the Daniel Rebour "presoftened" treatment, too...but others have said the alloy rails never get comfortable.
just noticed that mine has bigger hand-hammered rivets compared to the "99", maybe it's a "98".