If I recall correctly, in 1976, Jimmy Carter had a plurality of delegates , but not a majority, after the end of the primary season in 1976. Between the end of the primaries and the convention, the bandwagon started up, and uncommitted delegates, and those pledged to minor candidates, committed to Carter so he had majority support on the 1st ballot.
Also there was no guaranteed winner between Reagan and Ford heading into the 1976 GOP Convention.