In chemistry there are usually more exclusions than rules
Inorganic acids are usually written with H at the beginning of the formula.
Organic acids are written in many ways. Proton responsible for their acidity is a part of caroboxylic group. This group is usually written -COOH but sometimes -CO
2H.
Acetic (or ethanoic) acid is CH
3COOH, but it is sometimes written CH
3CO
2H or - even worse - C
2H
4O
2.
Don't bother, not formula counts but the molecule structure.