Oh yeah, what do you use to determine if a Pokemon's stats are shown? Like:
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Skorupi is used more but doesn't have its statistics expanding like Snorunt. It doesn't really matter since they're useless pokemon, but I'd still like to know.
Most likely this is because the Skorupi user did not have a full moveset. I can't say for sure, without looking at the logs (which I'm not going to do).
Battle logs can have all sorts of errors in them, and some errors can cause the entire stat collection program to crash. That really sucks when that happens, because it takes HOURS for this stuff to run. If there is a log that makes the program crash, I have to rerun the program in debug mode (which takes hours), find the offending log, fix the error or delete the log, then rerun the program again (which takes hours). It is the absolute worst part of doing these stats every month. And with half a million log files to process, you would be stunned how many weird errors come up. With that many logs, a "one in a million" error actually occurs with startling frequency. Log errors are a major pain in the ass.
Therefore, my stat programs perform certain basic checks before "accepting" a pokemon for inclusion in the detailed stats, which is where most of the heavy log processing takes place. These checks are not meant to be rocket-science, they are meant to eliminate a log at the first sign of trouble, so as to prevent the program from crashing. So there are a few things that I look for before processing a pokemon, just to make sure it looks like it read the log file correctly. The most common check that fails, is if a pokemon does not have four moves in its moveset. If there are less than four moves, the program assumes that there must have been an error reading a move somewhere, so it ignores all of the pokemon's details. However, it still counts that pokemon's usage, because usage is counted in a different program pass.
So, the idiot that used Skorupi three times last month, probably didn't bother to give the pokemon four moves. In which case, all the details for Skorupi were completely ignored. Or maybe there were three errors in the Skorupi logs, I don't really know.
The statistical impact of log errors, or idiots that don't give full movesets to their pokemon, are mathematically insignificant. So I don't spend much time worrying about them. The only reason I answered this question in such detail, was to give everyone an idea of how log errors impact the stat gathering process, and to explain why you might see occasional anomalies in the stat reports.