NAPS you are correct. At least some of these jobs are posted just to keep a pool of qualified applicants ready in case the job really opens up.
Some positions are advertised on USA jobs but the agency already has someone working for them who will get the job but by law they have to post it. This kind of stinks since you can waste aot of time and effort applying for a job that is already filled and that you have no chance of getting.
I should have mentioned in my earlier post that the advertised jobs that are already filled by existing employees usually are the better positions. Sometimes a hint can be in the job description/requirements which are written with such detail as to practically exclude anybody who isn’t already working in that specific type of position.