I too have often wondered at the /number or .number on Orrefors and Kosta glass. Since it does not make much sense to have 27 numbers of this vase I suggest that is unlikely. Similarly 27 versions of the shape would also seem unlikely.
So I pondered a while and have come up with what may be a possibility or two.
Possibility 1 - that seems somewhat unlikely, as duplicate numbers seem to exist, is that it was the 27th of that shape made.
Possibility 2 - is that it is an inspector's number. That is a person who inspected it for its correct shape, colour, etc. then engraved it with the appropriate number plus their own number verifying that it was saleable as a first.