Since I am absolutely insane and had nothing better to do, I went to the Death Star attack and counted the number of Rebel ships that took part in the assault and how many were shot down.
Initial shot in Yavin IV flyby: 30 or 31 (Approx 8 Y-Wings [some are too blurry to see])
Adywan's descent: 28 or 29 by my count (8 Y-Wings)
Number of ships according to Wookieepedia: 32 (22 X-Wing, 8 Y-Wing, 2 "Spearheads" [A-Wing prototype, not shown in film but in one of the games])
Total shot down in combat (Only counted are visible deaths. If the explosion is already taking place when the shot changes, then it doesn't count unless a TIE Fighter can be seen alread firing or flying to suggest it shot down a Rebel craft): 18 (5 are Y-Wings [3 in trench, 2 in dogfight])
Looks like Adywan got the number spot on and didn't exceed the body count in the extended dog fight scenes! 28-32 ships is perfectly reasonable to expect since I always saw the Imperial officer's "We count 30 Rebel ships" as a quick approximation. Most people would subconsciously round to the nearest 5s or 10s number instead of prattling off "We count 28 ships" or "We count 31 ships." It just sounds more natural.
Love the revisit.