The manual for the AF 280T says for TTL operation to first set the ASA speed on the flash unit. So it appears that TTL does not override the ASA set on the flash. It would have been nice if there had been an override setting on the flash, to extend the range and avoid having to set ASA on the flash (along with the possibility of forgetting to do so) when changing film speeds. I have heard the exposure compensation dial on the camera will change flash exposure--on the LX, anyway. I almost never use flash and haven't tried it, so I don't know if it can be used to effectively get a higher film speed.
The AF080C has no ASA/ISO setting, so the manual's TTL charts of usable f/stops within the flash range assume ASA 100, and say to adjust for other film speeds.