If posted, you can't edit them.  Corrections would involve posting reversals and re-entry.

And there is no way to Unpost them?  And is there a way that I can tell if they have been posted?

And there is no way to Unpost them?  And is there a way that I can tell if they have been posted?

Sage 100 is not a spreadsheet like system.  When you post something the data goes into read-only history tables (maintaining an audit trail of corrections by recording posted reversals and replacement transactions).

If the data you want to correct is not in a data entry screen (but showing up on the customer / vendor record...) then it is posted.  GL only corrections can be done with a journal entry, but to affect module data (AR/AP...) you need to do what I indicated, with few exceptions.  (AP Invoices can be adjusted without a reversal).

You unpost by reversing the checks.  You can tell if they have been posted by going into the vendor and seeing if the check is listed.