A lost favorite needs inside and none in the last .
That's the whole rule. Change it and everything below is recounted.
1
Fetch
Your public history is read from Last.fm, 200 scrobbles a page, and cached in this browser so the next visit only fetches what's new.
2
Count
Plays are bucketed per track per calendar month. A rolling window finds each track's hottest stretch. No model, no guessing — arithmetic.
3
Surface
Anything that cleared the bar and then went quiet is a flame, filed under the year it burned brightest.
Reaching Last.fm…
Nothing qualifies under the current rule.
Loosen it above: fewer plays, a longer window, or a shorter quiet period. Accounts younger than the quiet period can't have flames yet.