A corporate client on Broadhollow Road does not buy casually. It sends a purchase order with its own format, asks for a quote that matches last year's line items, wants an invoice that reconciles to its own system, and periodically sends a vendor security questionnaire. Each of those is a document that somebody at your end rebuilds from scratch.
That is the work worth looking at first in Melville, because it repeats on a fixed calendar and it is nobody's actual job. The assessment maps one of those documents end to end, where the content comes from, who touches it, where it waits, who has final say, and names the steps that must stay under a person's control before anything is built.
The pattern shows up most sharply at month end. The Melville office where month-end eats two days is the same workflow written out in full, with the parts that can be handed over marked separately from the parts that need a person reading them.