I use both of those sites

I specifically use footballdb.com for head-to-head history between two NFL teams. It reminded me that the Raiders didn't play in Pittsburgh for 20 years, from 1980 until 2000. The "Los Angeles Raiders" never once played in Pittsburgh. The teams played at Three Rivers 6 times from 1972 to 1980, including 2 playoff games. The Steelers won both playoff games, but the Raiders won 3 straight regular season games in Pittsburgh after losing the 1972 opener.

The scheduling formulas in place from 1978-1994 and 1995-2001 (very similar with some tweaks) created many oddities, including that 20-year gap in Raider visits to Pittsburgh, the Bears going to San Francisco far more often than the 49ers to Chicago (10-2 split in regular season games from 1975-2000), no regular season games at all between the Bears and Giants from 1977 to 1987 (and no Bears regular season games at the Giants from 1977 to 1995)---and weirdest of all, the Tampa Bay Buccaneers not playing a single game at Buffalo from their 1976 founding until 2009.