If you have played osu! mode (but not taiko/ctb/mania) in osu! maps, its rank won't display in taiko/ctb/mania.
The reverse is not true: taiko/ctb/mania maps display taiko/ctb/mania rank in osu! mode if you have played it.
The result is you see more A/B/C ranks than your A/B/C ranks in osu!standard and I found it annoying.
1.play a taiko/ctb/mania map
2.switch to osu!standard mode
3.select this map and it displays taiko/ctb/mania rank