Sorry to hear about your Smith.
Sealing the primers can help prevent squibs. Fingernail polish and any other primer sealant is not a 100% end all solution to squibs.
I have experineced squibs in factory ammo three times in the last ten years. Once with a Winchester 9mm round and twice with Hornady .357. I don't know if the primers on those are sealed or not. Ohio can be as humid as Guatemala, just not for as many months of the year. High humidity ruined a pound of H110 When I was loading .44 magnum rounds once. I experienced some squibs from that batch I loaded. I discarded the remainder of the rounds from that batch.
The difference between my squib experiences and yours being when the round went *pop* without noticeable recoil instead of *BANG* I stopped and inspected the gun. That attentiveness has prevented my beloved S&W, Ruger, and a friend's HK MP5 submachinegun from blowing up.
"9mm has a very long history of being a pointy little bullet moving quickly" --Sevens