From what I've seen, it is included in "sales" if it is linked to an invoice or sales receipt. So, if I create an invoice for the client to pay a $100 deposit in January and they submit that deposit in January, and then in March I create an invoice for $300 of work ($100 of which is paid from that deposit and $200 of which is a balance due), the "sales" are $100 in January and $200 in March, whereas they should be $0 in January and $300 in March.