What would "the 2021 school/fiscal year" refer to?

Sounds like, at least for fiscal years, this may vary from country to country. [or perhaps from language to language in which case my question regarding the English usage would still stand!]

To quote the current Wikipedia article for "Fiscal year":

In some countries, the fiscal year is denoted by the calendar year in which it begins and so in India, for instance, spending incurred in March 2022 would be part of the fiscal year 2021, operating on a fiscal calendar of April–March. In other countries, the fiscal year is denoted by the calendar year in which it ends and so in the United States, federal government spending incurred on 14 November 2021 would belong to fiscal year 2022, which operates on a fiscal calendar of October–September.

I.e. an example "2021–22" fiscal year might be shortened to "FY21" in India but "FY22" in the United States. Thus if using the end year is common convention in at least one of the American Englishes, my assumption that "SY21" refers to "school year 2021–22" would be wrong — "SY21" would instead refer to "school year 2020–21"!

UPDATE: I wonder if perhaps the India/USA distinction could be viewed a different way!? That is, the examples compare an April–March to an October–September range. The majority of time between April 2021 and March 2022 would happen in 2021. The majority of time between October 2021 and September 2022 would happen in 2022. Hmm… so if the fiscal year of India went from December to December would they still refer to it by the start year? Or if that of the United States went from February to February would they still refer to it by the end year? What then for a school year which tends to be a bit more balanced between its two calendar years? My answer is now more questions 🙃

In the US, the 2022 school year is the one that starts in 2021 and ends in 2022 (when the class of 2022 graduates). And fiscal year 2022 (FY22) is the same period, at least if you're an educational institution. The year officially starts July 1, though students start in late August or early September and end in June.

It is my job to know stuff like this. Nevertheless, I found some other examples from the internet at large.

• To jumpstart the 2022 school year, the USV/Schmidt Family Foundation presented scholarships to these eager students!

• Welcome to the 2022 School year — Carrie Jacobs Bond Elementary School

• Are you an upcoming Senior for the 2022 school year? PhotographyByChristy is looking for Senior's from each High School for the class of 2022!

Still, you should prefer to write out 2021-2022 when possible.