The earliest home VCR that was not a reel-to-reel machine and was available for the general public was the Cartivision. This machine had prerecorded movies available for rent, which could only be watched once, as the hardware necessary to rewind them was only available to retailers. Mostly available through Sears and Montgomery Wards, they retailed for about $1,350 and were manufactured from 1972-1973.
Betamax as we know it first appeared in New York and Los Angeles in September 1975, and then expanded its reach in January 1976. Its original price tag was about $2,295, with tapes that could hold 1 hour costing around $20-$25. Prices dropped in the next few years as the format war with VHS intensified, and we all know how that story unfolded.
Given that history, it's almost certain that the earliest home recordings circulating are from late 1975 or early 1976. The March 1, 1976 episode of the $20,000 Pyramid is from a home recording for sure. As far the 1973 Deacon-Ballard $10,000 Pyramid, that is likely from a U-Matic machine, which were generally used by TV stations.
-Flea