The canonical post numbers are those assigned by 8chan, and those numbers vary depending on the post being placed first in greatawakening (up to post No. 100 as I type this) or qresearch (numbers up to 402,000+)
The fact that one aggregator has a different running total could come from adding a post in error, starting at different points in time, or overlooking a post. I consider both (all three?) aggregators reasonably reliable, as each provides links back to 8chan - I've yet to find those links to take me any place other than where the Q post originally appeared.
There is just a lot of sensitivity that has developed around using one (or more) of the aggregator sites as being a complete and accurate collection of ALL of the validated (as they have been over time starting from 10/28/17 to the present) Q posts, and NO other posts; so that the general population can feel comfortable in relying on a given aggregator site (to read Q posts).
It seemed that a pretty high degree of confidence had developed around the use of https://qcodefag.github.io/ for that purpose. Let's hope that the new http://qanonposts.com/ will be proven to perform equally as reliably.