You want a perfect example since you are on FSD? DOAD.
Emperor Cow made a post on FB years ago one time on the expected sales of DOAD for the 3DS. From what I heard, DOAD sold roughly 300K+ copies, however KT was expecting 900K apparently which wasn't enough, DOAD was also almost the last game of the series from what Matt mentioned at one point.
No offense to DOA and may sound like i'm roasting the series for it, but DOA is not the holy grail of fighting games to net 500K like it's a cakewalk, especially on a 3DS for pete's sake (or games in general) and does not got it like that vs Pokemon.
KT conspiracy of poor handling of the series dates even back then. Remember that Shimbori had to "beg" for DOA5/DOA6 to even exist.
I can only guess that they expected that number because of how much past games sold (before DOAD), but they were crazy to assume it'd do anywhere near the same numbers as past games on an entirely brand new handheld-exclusive platform, and so many years after the last high profile game in the series on top of that. Its like they thought they were releasing DOAD on the latest Xbox just 2 years after DOA4.
And then they used that release to gauge whither or not the series was still viable in terms of sales... smh.
I actually always thought DOAD was a hit considering how well it did for being an early 3DS release and was always shocked that KT didn't follow up even on the Switch. I doubt most people would have believed a DOA fighting game could do as well as it did on a Nintendo platform.