Does anyone know why Baroque concerti, sonatas, and suites were often
published in multiples of 6 per collection - eg, Vivaldi's Il Cimento, La
Stravaganza, L'Estro Armonico, Bach's Brandenburgs, Bach's suites for solo
instruments, Handel's opp. 3 and 6, etc.?

A publisher's crochet?

Steve Schwartz