There is an interesting nuance to the stat for 1975/76. As you say, the Muller Road end was pretty big and their penultimate home game was us, on Good Friday if memory serves. The attendance was 26,000 odd and the overwhelming majority were in red. If we are generous and credit their attendance as 10,000 the 16,000 of us tipped the season average from about 9,100 to "over 10,000".
So for once it IS our fault.