When I was taught to spray lacquers years ago the rule I mentioned above was brought to my attention...doesn't matter if it's a top coat over a 1 week old sealer coat or 1 week between top coats...lacquer is lacquer and after a period of curing needs to be sanded just before applying a new coat. I was never told specifically why but after many gallons under my belt I came to believe the scratches help the new coat burn in/adhere deeper in the existent film.
what I can say is when I had a complete disaster situation that already involved some sickening amount of coats built up I found I had to strip it all and start over again...the following is replication of what destroyed the finish when I had fallen asleep: stripping involved putting 500W halogen work lights about 30" from the surface and leaving them there for too long at which point it basically melted the finish and allowed me to peel off layers (of about 18 coats by that point) of finish all the way to the mahogany...point being the layers and layers of built up finish were completely bonded an in essence one layer...and yeah, I followed the scuff it before applying new coats a week layer routine...I used 600 grit IIRC.