The FCC suggested the map is becoming more reliable with successive versions:
With the recent release, a new round of data is available from the FCC’s Broadband Data Collection program. The previous round of data represented networks’ mobile coverage circa December 2022. The new data reflects networks’ status as of June 2023.
In the coming weeks, I’ll share a new version of Coverage Critic’s maps incorporating the latest data and a handful of other upgrades.