while the battles of lexington and concord were the first shots of the american revolutionary war, which best explains why it might not be considered the first "official" battle of the war?

Experts say that they have no clue who official shot in the battle of Lexington

Explanation:

Some Red coats (the British side) wrote pamphlets of what happened at the time. They said that the colonists shot first in the battle of Lexington. On the other side the colonists wrote a letter that the British shot first. To this day experts can't say who shot first in the battle of Lexington.