I might not understand what triggers a retry but I would expect to see 70 430's in the logs,
one for the first try and one for the second. Then I would expect Newsbin to move on.
It won't even start retrying till the last file has attempted to download. So, seeing 430 errors doesn't trigger a retry. Understand that I'm talking about sets of combined files here. What happens after the last file in a set is attempted is that Newsbin counts down some seconds and then resets all the failed chunks that had 430 errors and tries to download them again. If you have PAR file, it'll also try to download PAR files. It's somewhat dependent on the presence of PARS. No PAR files, it'll try and when the retries are exceeded, it sends the files to the failed list. If there are PAR files. It tries harder by downloading the PAR files.
In 6.71B4, aggressive mode is really aggressive too so, after the retries expires, it'll assemble what it has of the file and then attempts to repair them.
It sounds to me like you're looking for some "early out" but that's not how it currently works.
430 errors are only fatal if you don't have PARS and have more then 10% failures. Otherwise, Newsbin can typically repair the files. The point of testing is to determine whether you have enough to repair.