deferred-revenue only captures what has been invoiced. A three-year contract billed annually shows one year in deferred revenue and all three in RPO, which is why RPO is the better forward measure for enterprise software.
Companies also disclose how much is expected to convert within twelve months, sometimes called current RPO. That subset is the number most closely tied to next year's revenue.
Example: Northwind Cloud reports $498M of RPO against $47M of deferred revenue, with $214M expected to convert within twelve months against $210M of trailing revenue.
Related: deferred-revenue, annual-recurring-revenue, backlog, revenue-recognition, footnotes