Average publishers increased from 127,000 in 1945 to 570,000 in 1955. (443,000 or 349%)
Compared with an increase from 1,034,000 in 1965 to 2,062,000 in 1975 (1,028,000 or 101%)
So yes a larger absolute increase between 1965 and 1975, but a much higher percentage increase between 1945 and 1955.
1945 to 1955 - 349% increase
1955 to 1965 - 81% increase
1965 to 1975 - 101% increase
So the early postwar period was the best for growth, even the decade leading up to 1975 did not match it.