The "simultaneous release" (sometimes called the "could have spent it") concept stems from the following principle, which is addressed in the Financial Accounting Standard (FAS) No. 116, Accounting for Contributions Received and Contributions Made (paragraph 17):

“If an expense is incurred for a purpose for which both unrestricted and temporarily restricted net assets are available, a donor-imposed restriction is fulfilled to the extent of the expense incurred, unless the expense is for a purpose that is directly attributable to another specific, external source of revenue.”

What does "simultaneous release" really mean?

• A department has both gifts and unrestricted funds (e.g., appropriations) in the fiscal year.
• This department has expenses (in unrestricted accounts) during this year.
• FAS 116 assumes that the department will use the gift funds first (that is, "could have spent it"), thereby “releasing the restriction.”  Since the restriction would be released within the same year, the gift can be recorded as unrestricted.