The differential is more than just a gear set, it contains an electric hydraulic pump, valves and a clutch pack. The early fluid change is to flush out the debris generated during break in. Honda was having some problems with fouling of these parts. The first change is around 15k on the MM. After that its a long time before the MM will want the diff fluid changed again.Happy to trust the maintenance minder. From what I gather, rear diff change will come on at 12,500 miles. Just trying to understand the need for the early change.
And if you have an oil change indicated by the MM at 12,500 it MAY throw the code for the differential fluid (as in, it doesn't want you to wait for the next oil change to change it).The first change is around 15k on the MM.