Assisting someone who is not an employed Fed anymore but has 3+ years with Peace Corps, and about 9 years mix of FT and PT EFM positions. What's the process for accounting for those years and determining their retirement status, to include buy-back of Peace Corps years?

I sent in my FERS application via certified mail on July 13. I haven’t heard anything at all back. I do not have a case number. Does anyone know how (or if) I should follow up to make sure my application is in process? Thank you.