So unlike how it looks, this isn't about a game going on sale. When this happens, it's about differences in regional pricing. Like a year ago, Poland was upset they were being charged the second most for games on steam, when they don't make that kind of income on average. So steam changed their regional pricing index, and games across the board got cheaper for polish users and a few other countries. Looks like they do this for recently purchased games when that happens. Not sure how many times this has happened, but I doubt it's very often.