TL;DRThe date range a line item pays for — shown on the invoice and used by revenue recognition.
Every recurring line carries a period start and end. For a seat product it is the schedule period, even when individual added-seat sub-lines cover shorter windows within it.
Recognition spreads the amount across those dates; collections does not care about them at all.
Where it happens in Sonic
Next
See it on your contracts
A walkthrough on the agreements and files you actually bill from — not a slide deck.