if you're using vault, make sure you have the factory member file also checked out, otherwise regenerating it will not work as it is write protected. You won't get a message from inventor for that so you can regenerate all you want.
Something that can force inventor to see you modified the model, and therefor require regeneration of the files, is simply to edit a feature. (For instance edit a hole feature by re-typing one of the values.) Then you'll be sure to need an update of the member files.