Graduate PLUS loans are aid year specific, so you cannot have the loan awarded across multiple aid years. A shorter loan period can be chosen if you only wish to apply for part of the aid year. If you decide to use Graduate PLUS to fund future aid years, you will need to apply and be credit approved each aid year.
Further, Graduate PLUS credit decisions are only valid for 6 months. This means that you can only request loan increases for 6 months after the initial application was submitted. You will need to submit a new application if you need additional PLUS loans after that period has passed. If your credit decision was approved with an endorser, you will need to submit a new loan application with an endorser addendum.