Further to the ISO rating & overexpose:(posted 8372 days ago)ANSI/ISO use a film developer that isn't anything any of us would use. They use an agitation technique that we don't use. They measure speed in a way not many of us find practical.
Manufacturer's don't up the film speed for marketing reasons--the standards by virtue of the procedures used force a film speed that isn't really practical. But it is "standard" that is, very repeatable and the procdure is very conducive to lab testing.
Note that Kodak and Ilford use EI indices in some of their new films. They don't claim ANSI/ISO. In my opinion, a better option. Give us a speed that really works--in general--rather than a speed that corresponds to lab processing we'll never use.