Almost.

I added a "Last Active Day" date field and used a process builder process (for both GL Account and GLAV) to populate it with the last day of the related Accounting Period so I didn't have to look through the accounting period object in my validation rules.

Rebecca, was the above your final solution?

Further question: Is it possible to put an optional filter on lookups to the GL Account and GLAV variable objects that only shows active options?

The object list for Financial  Suite above is incomplete:

Time Card Day should not be on  it but the following ones should:

• Accounts Payable(AP Override)
• recurring AP Lines
• recurring billing lines
• Bank Deposit
• Expense Lines
• Project tasks

My solution: I added a lookup to the  Accounting Period on the GL Account called "Inactive as of", and added a validation rule that requires that it be populated if active = false.  Then  on each of the above objects  I created a validation rule that checks whether the  GL Account is active  AND  whether  the end date of the Accounting period for the transaction is > than the end date of the "Inactive as of" period.

That formula keeps any record from using inactive GL-accounts, but do you have suggestions or examples of more nuanced validation rules that allow old records to keep their historic GL Account even if it is edited?