Adding to this thread, found it through a google search. Hoping that it will help others if they run into the issue.
Replaced heater core, then 2 weeks later replaced radiator.
Low coolant light stayed on, never went off.
Checked with a engine diag tool, no code. Reset battery and removed connections. Kept Adding coolant. Same result.
After 3 weeks and about 1200 miles later give or take, the light went off and on for about a day, and never showed up since. Could have been air or sediment, but in my case also it was just patience.