You do realize that the sellout streak started in 1966 (edit -- 1968; rest of post still stands), prior to which the team hadn't finished 1st in a division or conference since 1945?
Further context:
After 1945, not a single playoff appearance until 1971. Above .500 four times in that span (1948 7-5, 1953 6-5-1, 1855 8-4, 1969 7-5).
Initial DC Stadium capacity 49,219
Attendance
1961 29,784 61% W-L-T 1-12-1, last in conference
1962 38,505 79% 5-7-2 4th
1963 45,679 93% 3-11 6th
1964 48,984 99.5% 6-8 T-3rd (only game not a sellout was the opener, 1,642 under capacity)
1965 DC Stadium stated capacity per wiki 50,000, though numbers often exceed
1965 49,929 6-8 4th
1966 49,721 7-7 5th
1967 50,449 5-6-3 3rd in Capitol division
1968 sold out 5-9 3rd in Capitol division