Recently, I have had a number of people give me bags of old film. The expiration dates range from 1972-2003. Most of it is c-41, with a few rolls of B+W thrown on for good measure. I am not expecting much, but I plan on shooting it and having a bit of fun. The only thing I want to know in advance is a rule of thumb for exposure on old film. Some of the film was well stored, most of it not, but I am hoping that there is a rule for estimating what the likely speed of the film is now.
To be clear, I am not trying to turn old, bad film into sparkling, fresh film, I am just looking to not pump out roll after roll of black frames if I can avoid it.