Good eyes, Marc!
After reading your post, I went back through some images of the various backs, looking for just that, and found a surprising number of possibilities. Mostly, I was surprised that I had never really noticed that on Broadleaf class cards.
In many cases, it'd be a hard sell that isn't just faded, but I think you can make the case for a least a couple. Like you say, when you've got them in hand, it is distinctive.
I've attached scans of a couple of Broadleaf class examples paralleling yours - more of the Anon 3 cards show the brownish ink than the Factory 25, but it may not be exclusive and there's no obvious pattern as the sample size is tiny. Don't have these cards in hand to do side-by-side comparison, so the scans will have to do (all done with the same scanner).
Tyler, Rath - multiple copies each with Anon 3 - one each black, brown
Moore - Anon 25 (blk) ,Anon 3 (brwn?) ,Anon 25 (brwn?) , Broadleaf. The two Factory 25 examples appear different, though this seems more like fading/print quality.
Bauman - Anon 25 (blk) , Anon 3 (brwn).
Kutina - Anon 25 (blk), Anon 3 (blk?), Broadleaf (blk).
R. Miller - Anon 3 (brwn?), Broadleaf (blk)
