Hi, StdQC applies QC checks to loop packets and archive records before the StdArchive service ultimately saves archive data to database. I am only guessing having not seen your service, but I suspect that since you only have a single service your service is taking care of adding data to loop packets and/or archive records and saving the archive data to your database. If I have this correct then the StdQC service will check your data but since your data has already been saved to database your saved data will be pre-StdQC and hence unchecked. Should be easy enough to confirm, just run weeWX directly (http://weewx.com/docs/usersguide.htm#Running_directly) and you should see your data being properly QC'd.
What you may be better doing is changing your architecture so that you have a 'data_servcics' service that adds your data to loop packets and/or archive records and then have a second service at 'archive_services' that saves your data to database. This new service would be sub-classed from class StdArchive() and should only need a handful of lines to save your data. Of course if I have misunderstood your service then I may be completely wrong. If so it might be best if you post your code. Gary