Ah thanks, this looks much more usable. On the one hand, Photoshop's image model may be the only one which allows the same frame to re-appear at different points in time, but I can't help thinking this internal complexity must be awkward sometimes.
And if you do need something like this, an actual animation program is going to add considerable more choices, like "scripted" features where you say "scroll this frame by +100,0 over 50 ticks".