I doubt that there is anything wrong with automatic calculation. However,
it isn't all that difficult to confuse it.

Also, IIRC selection from a drop-down listbox does not flag the destination
cell as dirty to the extent that will trigger automatic calculation or cause
it to be included in a calculation. I seem to remember setting another cell
to the value of the drop-down box's target cell with a simple =n10 type of
formula, then using the second cell in my calculations. Rings a big bell,
but I haven't a clue where or when.

I also have a healthy distrust of local named ranges (i.e. the same name
defined in more than one sheet of the workbook). I'm never quite sure that
I'm really accessing the correct one.

Why not uniquely name each named range? Or possibly don't use named ranges
at all in this circumstance - merely use the A1 cell labels for the local
cells.