Do you use a conform tool at all?
Every turnover, even if it just a scene, should have an EDL with it so you can conform... eg one option may be you work on a scene by scene basis (ie a new AAF and QT for each scene) and then when a turnover of a whole reel or the whole film arrives, you can conform from the scenes to assemble the whole reel or film..... Justins Conformalizer app tracks VFX versions (if a standardised naming convention is used) so updates to VFX are not interpreted as new shots... and the correct material is conformed to the updates...
For investor screenings, it can be wise to basically maintain a constantly ongoing temp mix. So as soon as you have a scene in good shape, print stems of it & keep those stems on tracks along with your source material - then when you need to output a version you can conform the source material AND your stems & sometimes quickly patch & output a rough mix just from your stems...
ProTools 12 hour timeline is a massive advantage with such things...