Some trivia over crazy J fares, feel free to add and/or correct.
This year I have seen 2 crazy J fares.
In June AM MIA-GRU around $450
Now HX LAX/SFO-PVG/BKK/DPS $600ish
Airlines known to honor the deals - AM, AV, NH, TK, WY
Airlines notorious for cancelling/not honoring - AF, AZ, ET
The list above doesn't include official flash sales, routine low J fares (such as SV).