In the sentence, The company experienced strong year[-]over[-]year growth., how does the Chicago Manual of Style govern the hyphenation? Part of me believes that it falls under the "phrases,
'A year' can be any year without any specification. But 'the year' means a particular/specified year or the one which is already mentioned and thereby known. E.g: In a year there are twelve months. (means any year or all years) I was born in the year 2000. (in that particular year) Grammatically 'a/an' is known as indefinite article and 'the' is definite article. The indefinite article (a/an ...
Unless you're talking about Chinese (or Persian) New Year, the name of the celebration isn't New Year but New Year's Eve, and it happens on the last day of the old year.
From WordWeb: Annual: Occurring or payable every year What is the corresponding single word for occurring every two year, three year, four year etc. I understand that it's surely not exhaustively
When you say "the last year" you think of a row of things and you choose the thing at the end. When you say "the past year" you think that an event has gone by or passed. If I would look at Google N-gram Viewer, I think, that "in the past year" is less common than "last year". I would say it is a variant that can be found occasionally.
The word year when pronounced starts with a phonetic sound of e which is a vowel sound making it eligible for being preceded by an. Yet, we tend to write a year. Why?
I'd say 'across the year' hints strongly at sporadic events etc, whereas 'throughout the year' speaks more of consistent results. But this is opinion, and I doubt I'll easily find supporting evidence I can use to justify an 'answer'. You can check individual examples to see if my suggested rule-of-thumb seems to apply. As (I think) Lambie says, 'across my lifetime / several years' are probably ...