You don't have to have initiated a merge that later becomes a rejected merge, Sue. Just as any member can initiate a merge, any member can reject a potential match. (edit: I may be incorrect regarding the first sentence.)
Also, not all rejected merges started as pending merges. Some are created when we create profiles and we reject profiles with similar names as not the person whose profile we are creating.
I believe the intent of rejected merges is for them to remain in the system, reminding us that the 2 profiles are not duplicates.
Occasionally, a rejected merge may turn out to be duplicates; but most are 2 individuals with similar names or other data.
As for the Changes log, someone higher up will have to cover that.