For what it's worth:
Today (Sun 6/25) starting position:
Duration 91:46:23, miles 1025.9
Ending position:
Duration 97:22:34, miles 1102.9
Summary:
5 hrs 36 min 11 sec, 77.0 miles, 13.7 mph
Because the GPS tracking only showed details for the first 5.2 miles, there is record of the actual route for the rest of today's travels. It is unlikely that they rode their bicycles on Rt 81 since earlier in the trip they were strongly advised by the police to note ride on an interstate highway.
The "as the crow flies" route measures 71.9 miles. 71.9 miles added to the documented 5.2 miles, it gives you 77.1 miles, statistically equivalent to the stats provided by the GPS tracker. However, we know they didn't travel "as the crow flies", so the 80 miles cited by Darren in his video is pretty accurate. Because it is unavailable, the actual time of travel, actual mileage and actual average speed all remain unknown.