Maybe it's a prototype of a 70th anniversary set then. Of course, these days all those vegan bassists wouldn't only consider buying a gut set. But D'Addario could use their Zyex cores
It's strange given the fact that in a strings special of Bass Player 25 years ago, Jim D'Addario was very adamant about about a string having to be equal in diameter and mass-per-unit-length from one end to the other, in order to divide itself adequately into equal vibrating parts in the overtone series. But then, only a few years late they did optionally offer taperwound strings