Job Cost has no limit on how many periods into the past you can post.

If you post to the prior month or prior period, the Last month and Last period fields in the master file update. If you post to a period in the current year, the Year to date fields update. Any prior period date updates the Job to date fields.

Notes:

• If the entry needs to post to General Ledger, the period must be open to posting in GL
  • If you wish to post to a prior month for Direct Cost, Enter Billing, or Enter Cash Receipts, you will want to also open the corresponding GL period
  • See Article ID 35365 DocLink: How do I open a closed period in General Ledger? for those steps