Pre-audit = QC...checks/fixes/edits jobs (most of which you are pending to them on purpose) BEFORE they go the client. All the lines you send to QC for blanks or other problems count toward your 10% total for the week and affect your spot on the pay grid.
Post-audit = QA...checks job AFTER it goes to client, marking errors which are charged to you, affecting your pay on the grid. (These jobs are "randomly" pulled by QA, supposedly, just to check your accuracy.)
The extra letters and numbers seen with QA and QC (QC1, M Post Audit) don't change the above.