This is Bill (same name as your brother), and I am the Commodore of the Waterway Radio and Cruising Club
We have been putting out non-emergency boat watch calls on our Waterway Net
each morning (7268 kHz LSB). Also, the Maritime Mobile Service Net
(14300 kHz USB) has been putting out calls. The Cruisheimers Net
(8152 kHz @ 0830 ET) has been putting out calls as well. And, the International Boatwatch Network
and ShipComm have been asking their network to keep a watch for your dad.
As others have said, SPOTCHECK is not necessarily reliable from the mid-Atlantic and, of course, the device itself may be defective or may just have a dead battery
VHF range is about 15-25 miles at best, except for high-flying aircraft which normally would be monitoring VHF Channel 16 only when an emergency
or search and rescue
operation were active.
RE: routing, the usual route
from the Canaries
would be Canaries
to the Windward or Leeward Islands
(Barbados up to about St. Martin), then north toward New York, which could take many different routes.
A 26' single-handed boat is not going to make very good time, especially in light winds where sail-tending and sail changes are frequent. For a 72-year old, that will be very tiring. I believe 100 miles per day or less would be about the best to expect, even in favorable winds.
Bottom line: it's too early to tell for sure, but assuming he's in good health
and still sailing, it might well be that he won't make contact for awhile yet.
Fingers crossed. We'll keep putting out alerts on the radio nets.