Probably because everything about IBU is an estimate. There are a ton of of variables that final IBU depends on, not to mention perceived bitterness compared to actual IBU.
You need to try it yourself, see what you think about it and adjust accordingly.
Like many other brewing questions, you will get diffrent answers depending who you ask.
Stored dark, cool, and dry, they will last for months without a problem.
They were sold under the "Styrian Golding" name before. Now they are not allowed to do so but each must be sold under its own name.
There is no way to know what variant you bought.