Other than it being a “factory only release”, and that it was released at the same time as 7.13.3, I can’t find any other information about it anywhere. What’s it for? Does it backport fixes from the 7.13.x branch?
In general, the purpose of 7.12.2 was probably to fix some issue with 7.12 and 7.12.1.
It also happens to be the milestone or changeover firmware one needs to upgrade to from earlier versions including version 6 firmware when concerned about wifi.