This has been some years ago. Notably, I observed this in relation to search suggestions. You could enter a search and get zero results, but a day later or two, you'd get at least a suggested search term (regardless how accurate or meaningless this may have been). So I guessed, these were built up, at least partly, retroactively. With results now happily including these "sympathetically adjusted search terms" without presenting this as an explicit option, I'd guess, this may now apply automatically.