After Mack, went to get the cricket jam, went to check on Yoshi in Mario's Pad, then went to Kero Sewer, I didn't do anything out of the ordinary, opened all visible chests, skipped Black Shy Guy, used a Boo to climb to the pipe above the Save block, picked the Galaxy Coin in the purple room, defeated Belome, all without any death, and did Midas River, I did it 3 times to pick all Frog/Galaxy coins and Flowers.
Also, yeah, when I checked I had 42 Frog Coins alongside the 7 Galaxy Coins, I did get 20 Frog coins doing Midas River but I don't remember where I got the other 22 (Aside from the few that you can get during the waterfall part of Midas River).
EDIT: If it helps, I'm playing using RetroArch 1.7.2 with Snes9x 1.56.2 Core