Of course it didn't help matters having Bud Basolo Beefalo's founder say it was a "secret" how he got the fertile cross between Bison and bovine. He never revealed his breeder records.
Montanan Jim Burnett however, who was also on the ground floor of developing Beefalo was more than happy to share his breeding records. Burnett had a number of fertile 3/4 bison 1/4 Hereford bulls used in creating a quite a few of the foundation Beefalo bulls. These Hybrids were numbered 031 and 930. As a matter of fact, Burnett marketed semen on several bulls under the title "031" which may have also confused the issue, however these Bison Hybrid bulls produced a goodly number of 3/8th bison content (fullblood) Beefalo bulls by artificial insemination.
Right off the top of my head, I can list the great bull Columbus, followed by Tom Tom, Dakota Chieftain, Red Man, BCB Johnny Ringo, Dominion, Tartan, The Bear, and Hawkeye. All sired by Burnett's 3/4 Bison Bulls.
The Kreillings, who were part of the Hunt Brothers Clan in Texas owners of the Circle K Ranch had documented 3/4 bison-1/4 Charolais bulls that produced the popular Judd 806 And Warrior O7K.
So where did this 3/4 bison cow-domestic bull concept come from?
Probably from the Canadian Cattalo Experiments. The Canadians got their best results by breeding their Buffalo cows with domestic bulls. Somewhere along the line, Cattalo got confused with Beefalo. There was a big difference between the two. So were 3/4 cows used to develop Beefalo? There might have been a few. If you can name them, let me know.