I think it’s a bit simpler explanation. I don’t think there’s a differentiation between races for the chips themselves for Dopey. You have two chips, each encoded with the bib number, with one on each bib. That’s why people who inadvertently wear the wrong bib on the wrong day still get recorded correctly, at least in the instances I’ve heard of. Some of the chips were just inactive due to a manufacturing error.
The reason for the “wear both bibs” directive was likely due to the fact that they knew only one of the pair was likely to be inactive, but the corral assignments were different between the two sets of races. They couldn’t just have people wear only the 5k/10k bib for the marathon, as they would’ve potentially been in the wrong corral. So the 5k/10k bib was needed to provide the active chip and the half/full bib was needed to provide the corral.