I think I asked a question that was similar, but this question is different, because the context is completely different. One of the issues is that sometimes you waste 10 panels doing a simple exposition, like when you write a scene for a mission briefing. Could you do a one panel flashback to a scene that was never shown after the first panel of a mission?
Let me illustrate both options:
Option 1:
1, 2, 3, 4, 5, 6, 7, 8, 9, 10 (mission briefing) > 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 (actual mission)
Option 2:
11 (actual mission), 5 (flashback) 12, 13, 14, 15, 16, 17, 18, 19, 20 (actual mission)
Option 2 saves you 9 panels. Panel 5 is shown as a flashback in option 2 even though it was not shown before. Is this totally ok? I think I remember seeing something like this before, but I don't clearly remember it being an actual thing. I am not 100% sure.