I don't have old exposed film to try, but I do know that old film recently exposed needs heaps of exposure.

I use mid 60's long frozen film, that statrted as 100 iso. It is now around 12 iso in sensitivity, and needs 18 minutes in straight d-76, 20C, 30 seconds interval of 2 second agitiation with no additional anti-foggants to get anything like a normal gamma for the processed film.

So you say 'per directions' - do you mean some old film processing threead instructions, or the package directions?