Sparky, I'm sorry but I don't completely understand about the different ISO's. There are a whole bunch of different ones for the same film. Are these development times for those who intentionally shoot the film at a different ISO and therefore a different development time? I am not clear. Take a look at Ilford Delta 100 Pro for example. What would I follow if I were doing it all as an average no special effects roll.
A given film might be 'rated' by the manufacturer at, say, ISO 100, but there's no law that says you
have to expose the film at ISO 100. You're free to rate it at 25, 64, 125, 80, 50, 120, 320 or even 400 if you wish. Using ISO 100 is the manufacturer's
suggested starting point.
If you find exposing it at ISO 100 tends to overexpose your images
given your gear, your metering & exposure techniques, all in combination with your processing the film (time, temp, developer, mix ratio, agitation etc), you would want to increase
your rating of the film to 125, 164 or even 200 in order to get better results.
On the other hand, if you consistently get 'thin' (underexposed) negs, you'd want to drop your rating of the film to 80, 64 or even 50, whichever gives you the results you want.
Shooting film is a lot like cooking. You might find a great recipe for something you like to eat, but that's far the the ONLY way to prepare that particular dish. You're free to change the temperature, time, seasonings, etc. To suit your palate. The film manufacturers give you their suggested recipes, but there's no law broken if you alter it.
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