It kinda makes me wonder if you were supposed to originally start with 0 hearts in CV3. So yeah, we all know or should know you need to destroy at least 3 candles before a weapon upgrade will appear in place of a small heart. But you also need 4 or more hearts already. So if you have the flail and want to upgrade to the morning star, you need to make sure you don't waste all your hearts between upgrades, or else you'll never get that last upgrade.
I never knew that. I was wondering why in one of my play sessions it seemed like weapon upgrades were never dropping (I got dagger-happy).