Vertically misaligned margin note

adding \mbox{} (or \leavevmode) as in:

\newcommand{\years}[1]{\mbox{}\marginnote{\footnotesize #1}}

will fix your alignment (although all the lines ending with \\ look very suspicious (and generate warnings about underfull boxes)

This works because the alignment works best if the float is tied to the paragraph, so if the insert is in the first line rather than before it. It then automatically aligns. If you put the insert in the vertical material before the paragraph you can fix up the vertical spacing but especially if you are changing the vertical spacing mid document, it's harder. \mbox just forces the paragraph to start with an invisible box, so the insert happens within the first line. It would be enough to use \leavevmode (which is used in the definition of \mbox as you do not need the box here, just to force the vertical material to end and the paragraph to start.

I won't delete this answer, because of the comments, but I do encourage you to read the other answer, which is considerably better.

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I believe this is because you "need to start the paragraph" before starting the marginal. You can do this:

\newcommand{\years}[1]{\hspace{0pt}\marginnote{\footnotesize #1}}