For electronically filed SECTOR tickets, tech support might be able to give you the “last modified” time for the ticket which would indicate when it was filed. Usually they are uploaded/filed promptly so the late filing defense doesn’t usually work anymore.
You can try contacting the King County Prosecutor’s office. If a prosecutor is present there usually will be an opportunity to speak with him/her just before your hearing starts.
You are correct that arguing circumstances will often not work for contesting, assuming your ticket is not for speeding. However if it’s a speeding ticket your best defenses would involve preliminary motions to get device evidence suppressed due to insufficient device testing or certification. Also if your ticket was after a collision not witnessed by the issuing officer, you might have a defense if no actual witnesses are present at the hearing.
If you want help reviewing discovery, upload digital photos or scans (with your personal id and citation number redacted) to any free image hosting site and link them here in your thread.

