Both "Yaoi" and "Shounen-ai" are considered unused terms in the Japanese fandom. Here in the West people still used them, but it is not clear when one begins and the others ends; for this reason, I believe that using only "BL" for any Boys' Love manga that would otherwise be categorized into either yaoi or shounen-ai would be better and avoid any kind of misunderstanding.
Even on websites like MAL, where they also use both of these terms, it is clear that there are not many ways to distinguish the two, since many manga have both tags (for example: https://myanimelist.net/manga/66057/Blue_Sky_Complex)
BL is a more modern and simple term, since it can be seen as an umbrella term for the other two.
Here are some sources that explain this better:
Also, I would like to point out that anilist is already ahead of us and no longer uses any of these terms, but only Boys' Love. They also only use Yuri for works that depicts wlw content.