The 1990's Cowboys were not a dynasty, imho, they were really good from only about 1991 to 1996, to me a dynasty has to go at least 10 years. By putting your list by decades starting with 0's, you can't include the Cowboys from 1966-1980.
If you only are figuring dynasties after the league merge, that's different, you didn't say so though. And I'd still not include the 1990's Cowboys, like I said, not long enough of a span of being very good.
But I would also add the Cowboys to the Steelers for the 1970's, from 1970 thru 1979 the Cowboys were in the Super Bowl 5 times, twice in the NFC championship game and twice in the divisional round, to me even though they only had 2 SB wins, to be in the hunt that many times is still a dynasty...