therefore, if a particular symphony or concerti is still in the MS format, chances are that it has never been performed or recorded.
Not at all. A great many works exist only in MS score with the parts not printed but written by a copyist or copyists, yet they have been performed and continue to be performed using those parts. And copyists' parts are perfectly usual for many works where the full score has been printed, though the string parts (on the whole) tend to be printed - which is why these are sometimes the only parts of some works which survive. "Published" does not, of course, necessarily mean "printed".
