The last time 6th place had more than 74 points was in 2009/10, our relegation season. Huddersfield finished 6th with 80 points. That said, Southampton in 7th finished on 73, so from Huddersfield's perspective 74 would have been enough.
http://www.statto.com/football/stats/england/league-one/2009-2010/table
At this point in that season, 6th placed Huddersfield were already on 54 points, 5 more than us and 4 more than 6th placed Millwall, so they only gained 26 points from the remaining 15 games, very similar to the 25 points we'd need to get to 74.
http://www.statto.com/football/stats/england/league-one/2009-2010/table/2010-02-20
It does seem that 74 is a good target to aim for, although there's always the odd season that can mess that up.
Interestingly in the 2009/10 season, Millwall were just outside the playoffs, 11 behind 2nd placed Leeds but rocketed up in the last 15 games, taking 33 points and being just 1 point and 2 goals away from snatching 2nd place from Leeds. Didn't matter though, Millwall's form led them to win the playoffs.
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For us to reach that 74 points mark, getting 25 points over 15 games could look something like this:
7W 4D 4L or 8W 1D 6L.
We're effectively aiming for 8 wins from 15 games, or 7 wins with only 4 losses along the way. Good to keep in mind that it shouldn't be doom and gloom if we lose a couple along the way.