18. I'm trying to use data from the CORS site BLYT and/or others in Southern California and there is only the observation file (99o). I would like to process my GPS data using this site. Why is the navigation file (99n) missing?

Some regions may use only 1 navigation file for the nearby sites or the navigation file is not in the directory where the the observation file resides.  National CORS does however supply a global navigation file which can be used for processing.  The name of this file is brdcDDD0.YYn, where DDD is the day number and YY is the 2-digit year.  You will find this global nav file up 1 level from the obs file.