1: It's from the FAA
2: Your PI number (Pathology Index) number is your special-issuance FAA file number. Put this on everything you send the FAA, along with your name and birth date.
3: The duration of the authorization is at the top
4: The first paragraph lists
- The diagnosis or condition covered by this special issuance
- The fact of medical ineligibility
- The granting of special issuance
- The duration of your present medical certificate.