I try not to plant either until after danger of last frost is past which is May 15 to January 1 here.
When I do plant something a little bit early that might get hit with frost I try to put loose
hay around it and over the top of it carefully. They can still get light and grow through the loose hay but when you get a light frost they are somewhat "more" protected from it as the frost tends to hit the surface of the hay and not go very deep within the hay.
Maybe you could try this on your remaining plants until you are safe from frost.
Here it is a gamble no matter when you plant as I have seen overnight lows of 22F the first week of July, so I "always" plant expecting frost here.
As for why one was hit harder than the other some very "small" things can make quite a big difference. Early morning light can save some plants if they getting direct sunlight earlier than other which warms them
enough to help save them from the frost. Other plants a few feet away blocked for 20 minutes longer from direct sunlight may be affected more profoundly by the frost. Here I try to keep all of my gardens facing the east so that they get the earliest direct sun possible to help combat late frost damage. I also try to plant my plants according to height so that they are not blocked from direct sunlight in the morning by other plants.