You are correct in your exposure and development considerations. Typically the EI of a film is not a stationary number. As one moves into expansion of contrast on a film the EI increases and as one moves into contraction of contrast on a film the EI decreases.
Originally Posted by Sean
For instance with Efke PL100 I would rate the film at EI 50 at a SBR of 7 (normal). If I had a scene with a SBR of 8 (N minus 1 appr.) I would still rate the film at 50, When I get into a SBR of 9 (N minus 2 appr) I would rate the film at 30. On the other hand at SBR of 6 (N plus 1 appr) I would rate the film at 80 and for a SBR of 5 (N plus 2 appr.) I would rate the same film at 100.
Regarding low value placement, John Sexton is reportedly to have said that "nothing lives on Zone III". I would guess from that comment that he doesn't place his values at III.
I use incident metering exclusively today. I have a spot meter but just don't use it anymore.