The frame data lists "KD" on purpose for moves that knock down, it's not an oversight or mistake. If a move is listed as -10, that means you can hit it back with a move that has 9f startup or less. If it's -20, you can hit it back with a move that is 19f startup or less. So if it said -250 or whatever a knockdown is, it sounds like you could hit it back with a move that is 249f startup or less, but you can't. The exact number isn't even important when it's that high anyway. So simply saying KD is the most straightforward and helpful thing a KD move can say.
Throws whiffs do show frame data. Normal throws are 3 / 4 / 18, for example. If they connect and knock down, they should list KD, as mentioned above. Midori's normal throw doesn't knock down, so THAT should list an actual frame advantage. It doesn't now, but that's just a bug. It will eventually be fixed and then you'll know the frame advantage after Midori throws.
White moves are invulnerable to strikes. We don't list throw invulnerable, not because the intent is to hide it, but because it's just too visually busy to show it. Characters themselves and numbers have to be two-toned all the time? One color for strike invulnerable AND also, at the same time, a second color for throw invulnerable? Or they need to have one color for throw invuln, one for strike invuln, and a third color for throw+strike invuln? We feel that's a visual mess when combined with the other colors we already have to show on characters, so we display white for strike invuln (that's most important), blue for armor, green for parry, purple for poisoned (not in the game quite yet but will be), and that's it.
I'm not sure how we'd display gaps in a string or how to precisely define that. What about doing A, then another A as soon as possible? That counts as a "string" or it doesn't? For that you can already compute the size of the gap. And does A, then A again count as a string if you waited 1f longer than you needed to for the second A? Or are neither of those strings and this is only for when you cancel one move to another? What if it was a normal move cancelled to special, does that count? Anyway, if we knew what to compute and what to display, we could consider adding this. Though the priority right now is on new content(!), things for beginners, and improving online play. Things for bleeding edge experts like frame data, we can keep in mind for later in development though. We'll also continue to fix any bugs we find in the frame data display.
We hope you like the frame data being in-game by the way. That it's dynamic and shows the correct, different numbers if you hit early or late, if you jump kick high or low, etc, is not even usually shown in fighting games. It's really useful!