This Is what I think
May 1963- JFK in a landslide over any Republican candidate
May 1967- George Romney taking down LBJ
May 1971- Nixon barely winning reelection
May 1975- Jackson or Ford beats Ford in a landslide
May 1979- Reagan or Kennedy(Tossup) (Carter approval were in the low 30s and until the Iran hostages Kennedy was consistently polling ahead of Carter)
May 1983- Reagan in a close race over Mondale
May 1987- Hart over Bush
May 1991- Bush in a landslide against any democrat
May 1995- Dole over Clinton(Clinton's approval were low)
May 1999- Gore over Bush decisively(Clinton's approval were skyhig and GOP were low)
May 2003- Bush in a landslide against any democrat(Iraq was thought to be won)
May 2007- Hillary in a close race over Guiliani
May 2011- Obama over Romeny
May 2015- Hillary
I agree with you for the most part. I seem to remember that the consensus in 2011 was that Obama would get defeated in a landslide by Romney, as the economy was still mediocre at the time.