I can't say for sure if your cory starved to death or if it was do to another cause.
Do the corys look really skinny (particularly look at the belly area)? You can examine their poop as well.
Corys normally feed openly. They usually aren't afraid to come out, venture around the tank and eat while the light is on, they don't have to wait for the light to turn off.
Having only 2 corys might explain them not feeding openly. They might be stressed out because their group is too small (they are a social fish and should be in groups of at least 5, and you have the room for that many + more).
The corys could be stressed for other reasons, maybe sick with some infection, or has internal parasites/worms. Or maybe it is afraid of the tankmates, you, or whatever, causing them to be stressed and not behave and feed as normal.
If they aren't stressed, but are hungry, you would see them venturing around, sifting around, trying to find food. If they are starving/skinny, and you don't see them doing that, then they are stressed for one reason or another.
You can try spot feeding (dropping food directly near corys) and/or just feed more. People worry about overfeeding, but really, as long as you have enough biomedia, then that extra food really is just extra bioload and the filter should be able to handle it, just like adding more fish (bioload).
I've seen the difference in feeding behaviors in fish that are fed too much, just enough or too little. If your fish are "super excitedly"/chaotically gobbling up the food, then that is too little (they are seriously competing for the fish as to not starve, because they know, not enough gets fed to everyone, which then leads to the less competitive fish to starve -usually bottom dwellers and "shy"/slow-eating fish). If the fish rather ignore the food and a lot goes to waste, then that is too much (not hungry/already full, assuming they do eat/like that food). They should gather and calmly/peacefully eat together, and not have it look like a store opening Black Friday sale stampede/rush. You don't have to feed so much that all the fish are stuffed full, but all fish should be fed enough that they don't have to compete or starve. Even if you have slow eaters/grazers, there should be enough food left after the faster eaters get their fill. Nocturnal feeders as well, but it would be better to feed at night just so the food isn't "rotted" by the time they get to it.
By the way, Corys pretty much eat anything, so if they aren't eating, then they probably are stressed or sick. (fish can stress to the point that they don't eat and starve to death).
And corys really are not that shy and normally eat their share of food even if snails and shrimp are feasting on it.