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Presequel
Prequel?
Presequel was used by the Borderlands game that comes between 2 and 3. In the same vein, Andor/Rogue One are the sequels to Episode 3 and the prequels to Episode 4.
So an interquel, then?
I would call it an “insert”
Let’s just renumber them all again, so Rogue One is 4, Andor is 5, and A New Hope is 6. That makes Empire 7, proving the OP correct.