They includes 3rd parties in 2016, but did not in 2020 and 2024, hence the different margins. And the 3rd party they included was of the Republican spoiler type rather than the Democratic spoiler type
They had way higher third party votes in their poll than actually occured - and the third party votes in 2016 were higher than usual (helping trump narrowly win in 2016)
They includes 3rd parties in 2016, but did not in 2020 and 2024, hence the different margins. And the 3rd party they included was of the Republican spoiler type rather than the Democratic spoiler type
They had way higher third party votes in their poll than actually occured - and the third party votes in 2016 were higher than usual (helping trump narrowly win in 2016)