As I understand ranks in chat aren’t overall ranks either, it’s the category ranks which are famously lower than overall rank.
The old Elo remnants exist somewhat under codeword “egf”. For Koba’s game T:3183 R:1 (ennuiaboo vs KoBa) we get 742 → 742 / 100 = 7 → 7 + 9 = 16 → 30 - 16 = 14k!
Or the game that was played right after this screenshot A short travel through OGS history - #28 by DVbS78rkR7NVe was taken: correspondence egf=1685.58 (matches the screenshot) → 1685 / 100 = 16 → 16 + 9 = 25 → 30 - 25 = 5k!
Again these are category ranks.