Forward-canon: the Division-organized roster is canonized at Marineford — 16 divisions, each with a Commander (Marco the 1st-Division, Ace the 2nd-Division, Jozu the 3rd-Division, Thatch the 4th-Division (deceased per Ch. 159 Ace reveal), Vista the 5th-Division, etc.). The Division-Commander structure is the franchise’s load-bearing non-flat-pirate-crew hierarchical model (compare to the Roger-Pirates flatter structure or the Beast-Pirates Tobiroppo / Six-Gifters hierarchy).
Why this matters
The Whitebeard-Pirates Division grammar is a load-bearing organizational pre-load for the entire forward-canon Yonko-crew architecture. Oda installs the numerical-division hierarchy through Ace’s casual self-identification, without explanation — the reader is expected to absorb that Whitebeard’s crew is large enough to need numbered divisions. Forward-canon: this scales to 1,600 crew members (16 divisions × ~100 each).