Think of it this way, in a federated system of multiple interacting instances running multiple different mostly overlapping softwares the question of "how many total posts are there?" and "how many total comments are there?" can only be answered with contextualized statistical observations that attempt to estimate a value that at a philosophical level may not even be establishable as a precise question... which isn't even getting into whether you include really creepy/toxic insular communities on the fediverse or not which is an ethical, cultural and practical question with many grey areas and details.
Also, remember this is all at least to a certain extent opt-in statistics (as it should be) so you can't expect you are sampling the entire signal... which means that stepwise offsets like this may just indicate differences in how much of the signal that can be observed that arise from changes in how instances federate, report information to bot crawlers and quantify posts and comments themselves.
