Interesting set.
Without any intent to rain on your parade, I will point out that the box and the pieces in it do not match. The box is for a Quick Disconnect socket set. That's what the "Q.D." on the decal refers to. The pieces inside the box are Lock-On, as you already know. You didn't say anything about that, so I am not sure if you recognized it or not. And nobody else said anything, so I guess I am the unlucky stuckee who can say something or keep looking at the king with no clothes.
I will hasten to add that it does not detract from the set. It may even make it more interesting as a conversation piece.
As you may already know, Q.D. sockets and tools preceded Lock-on sockets and tools. Their set numbering scheme was agnostic. The "13" refers to the number of pieces, the "P to the type of box, and the "D" to Double-Hex. Blackhawk made 13PD sets in the Q.D. era, and 13PD sets in the Lock-On era, and, there was a time in the mid-30's when they were making both, still offering the Q.D. socket drive tools, just like they were still offering all their early fixed socket wrenches in black satin finish, but in the back of the catalog.
The way I see it, there're two possibilities here. Someone either replaced the original Q.D. pieces with Lock-on pieces, or, perhaps Blackhawk actually shipped some sets out this way when they ran out of boxes with Lock-On labels. EDIT: Better yet, to use up a surplus of older boxes with Q.D. decals when they finally discontinued the Q.D. line.
Again, either way, nifty set.
Discontinued in the mid-30's after they added a captive push button inside each hole.