Well, to get a little more nuanced, generally when people say “$ABC comping from xyz” they mean “if its relative sales from here until day 0 match xyz, here’s what the comparison to xyz final sales gives.” So like, using the same reference movie for remaining growth pace and for final sale:gross calculation. Which is convenient, but not really logically required in any way.
I think the latter becomes outdated more quickly, whereas the former is more sensitive to raw size/hype/intensity of day1 rush and such. So I would probably reject any 2021s for pace, and reject any 2019 or older for final sale calculations, and want to stick some 2019 trending patterns into 2021 final sales ratios.