I did wonder. It's annoyingly difficult to find lists of all-time English football records, everything refers to 'of the Premier League era', albeit it does appear Chelsea's 86-game unbeaten home run under Mourinho is an all-time English league record. Liverpool's 51 is second since the Premier League's inception.
Reading once held the Football League record for home games without defeat: 55 set in 1935. Millwall beat the record in 1967.
Got it! The previous top flight unbeaten home record was Liverpool who went 85 games unbeaten from 7 February 1978 to 31 January 1981.
Ridiculous you have to do extra digging as all the media think football only started in 1992.
I started looking but gave up for precisely that reason.