If we continue to fund the Navy billet in FY20, is that a violation of the bona fide needs rule?
Based on your story that the Air Force has been providing funds to the Navy to supply a GS 14 BFM in FY 2019, but has subsequently hired an AF GS 14 for FY 2020. Also, the Navy agreed with the AF that when an AF GS14 was hired, the Navy would relocate the Navy GS 14 to another Navy unit. Your question was if we continue to fund the Navy billet in FY20, is that a violation of the bona fide needs rule? I would review the budget documents that were submitted by the AF in regards to funds for FY 2020. Based on the reasons Congress was given to fund the program may help you assess the use of funds, e.g. did the AF tell Congress that funds would be used for a Navy GS 14?.
The next course of action I would strongly suggest be taken is to contact the local Comptroller or Comptroller designee with the situation and ask for guidance. As a Financial Manager, one must be aware of all fiscal laws/policies to adhere and protect the program funds and execution.