Right, the blank is an old one that has never been built on. So it is a new build with old stock. Such blanks are in varying conditions of preservation, so you want to take that into account when you wrap the ferrules etc. Such blanks are always a gamble, it could break the first time you cast it, or fight a fish. Most of the time they are OK.
It is the same thing with a new blank, there could be damage that you can't see, and that is where the rod fails. It may not fail the first time you try it, but it eventually will fail. That is why new blanks have a one year factory warranty.
Old blanks that have been kicking around for a while, could have been abused in all kinds of ways while in storage. And, the ultimate question that always bugs me is: Why wasn't this blank built-on years ago. Could the original rod builder have rejected the blank because it had some kind of flaw? Yes, using NOS blanks is not for the faint-hearted.