The second and final year gives the impression that you mean one specific year, which was at the same time your second, as well as your final year. For example: In the fifth and last year of the war, the motivation was dwindling. Of course, in your sentence, this interpretation is impossible because you use between, but I did get confused at first.

Understanding the Context

'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.

Key Insights

(in that particular year) Grammatically 'a/an' is known as indefinite article and 'the' is definite article. The indefinite article (a/an ... Is "tri-quarterly" a real English word meaning 3 times a year? Are there any other words that mean 3 times a year? A year-end review is a review of something held at the end of the year.

Final Thoughts

The year in review could be used as the name of this year-end review, but it can also simply be a phrase describing the period (one year) that is being reviewed. "Year-end review" or "Year in review"? - English Language & Usage Stack ... Is this the correct spelling of year's in this context? I'm not a native English speaker/writer, but I do consider myself fluent, and this spelling tickled something in the back of my brain. If it matters, the report format only displays a maximum of two years at a time (this year, and last year).

2 Is “this last year” proper English? Yes, it means "in the 12 months prior to today" This contrasts with "last year" which [currently, and in most contexts,] refers to the whole of 2019. Have a look at the examples given in Google Ngram Viewer. meaning - Is "this last year" proper English?