Ok, well, here is the story.
I bought a bag mag from eBay from a camera seller. It arrived, and only had like 5 septums. They gave me a partial refund, and I kept it for parts. The leather on the bag was really nice, and the holder itself was in great condition, but it has a cardboard darkslide which is showing considerable wear.
I got two more off ebay. One good and one listed as parts. Both in stated condition.
The good one also has very supple leather, and came with all the requisite septums, however one or two have the wrong numbers. The red window is also very very dark (possibly replaced?) and it has a normal plastic dark slide, which has been repaired. The mag has been repainted, but that doesn't bother me as long as it works.
The second one, came with 10 septums of noncontinuous numerical order. The leather is a little dry and is white in some places, but otherwise intact. it has no darkslide. Some of the septums are corroded.
Obviously, I'm going to want to replace the darkslides and treat the leather to preserve it and keep it supple. I tried using a standard 4x5 darkslide, and no dice, it's too wide. How does one cut the darkslides without them cracking? What should I use for the leather?
Would it be simple to just paint the correct numbers on the misnumbered holders? For the missing septums, I have a couple fubar graflock grafmatics I can steal septums from, and paint numbers on. I like the bag mag design better than the grafmatic one so far (do they make graflock bagmags?!), it seems a lot less picky and easier to load, with more capacity. but I haven't used it yet, so i'm reserving judgement.