Our loadsheets cover all flap settings. There's a trim setting for 26K Flap 1-5, then another from 10-25 (from memory there's only two divisions), and then the same for 24K.
FMC trim for a given CG changes with thrust setting 20/22/24/26/27 and flap selection, but not when an assumed temperature is being entered.
Manual load sheets in FCOM tables give corrections to a uncorrected trim in a more basic manner, thus are not as accurate but well within tolerance limits, thus used, a simplified method.
It would be much more "messy" for Boeing to publish in AFM a large correction table which is then to be used by airlines listing each thrust and flap setting combination rather then to average several similar approximations into a single value when possible thus minimising pilot correction values listed on loadsheet for simplicity.
The FMC and OPT however are not restricted by such limitation and thus provide excellent indication of trim usually within 0.1 of each other as they use a digital file containing all corrective values.