A320 Maintenance technician reported an engine pylon was deferred although it exceeded the limit for missing fasteners.

Narrative

At XA:52 I was assigned a task for Aircraft X. I verified that eng 2 pylon panel had one fastener missing. I contacted Maintenance Control and notified them that we were out of limits per AMM (Aircraft Maintenance Manual) 54-XX-XX-XXX-XXX. I was given a deferral reference of Company Repair Document 51-XX-XX-X. I reviewed the criteria for dispatch with a missing fastener and determined that we were within limits for a deferral and created a monitor. At XB:00 I was contacted by Person A and told that this Company Repair Document reference could not apply. the number of discrepant fasteners may not exceed 10% of the total. Panel 425al has a total of 4 fasteners meaning 25% are missing.Cause: I was assigned a Right start on Aircraft X. It was notified close to departure time when notified of a missing fastener. While working with the Maintenance Control I reviewed all relevant material (AMM and Company Repair Document). I clearly missed the 10% limitation.Suggestions: Work slowly; deliberately; and focus on all details