Learned a whole lot from my friend. The cell carriers never wanted this information public. But the Biden FCC released the information publicly based on actual signal measurements by an independent party. However once Trump's people took over the FCC it was pulled down and a map was produced based on carrier reported data that is highly inaccurate.

He told me that the map I found is 'optimistic' and based on proposed license data. He did say it was pretty close at the zip code level but he wouldn't trust it anywhere else. Hope that helps.