In this case I believe it is non-severable and PoP starts in August same FY as appropriation.
1. Services are considered severable if they can be separated into components that independently provide value to meet an agency’s needs.
2. Non-Severable Service. Services that represent a single undertaking that cannot be feasibly subdivided. If the services produce a single or unified outcome, product, or report, the services are considered non-severable. Requires the contractor to complete and deliver a specified end product.
DoD Financial Management Regulation Volume 11A, Chapter 3
030404. Appropriation Policy
4. Because research and development test & evaluation (RDT&E) requirements are iterative in nature, RDT&E programs, projects and activities are not subject to full funding policies. For example, DFARS 232.703-1 permits DoD organizations to incrementally fund a fixed-price contract if the contract is funded with research and development appropriations. Similarly, DoD budgetary policy Volume 2A Chapter 1, Paragraph 010214 provides that RDT&E budget estimates are prepared on an incrementally funded basis and only those funds required for work in a given fiscal year shall be included in the RDT&E request for that fiscal year. These policies apply equally to budgeting and obligating for requirements that in execution involve placement of Economy Act.