thanks for the link
At your link, aren't those ratings of all the cell providers though? ( Charts in blue, showing how many bars with Verizon etc )
The reviewers are the ones I would rely on to verify if cell coverage is good or not. I've had plenty of experiences all over the US where charts like that have been completely and totally wrong. In the reviews I saw a Consumer customer and an AT&T customer both complaining about coverage in the area. These customers have nothing to gain by lying about cell service in Fort DeSoto, so I would trust what they said before anything else.
However, we still don't know where the Laundries were between checking out of the Ft. Desoto Campground on Sept 8 and the night of September 11. So we don't know if they had cell service or not.