Getting the charts together to make this involved a lot of lookup formulas to draw info from other spreadsheets. Now, most of the time, when I inserted a function to draw in the level of a book, say "N", I remembered to tell Excel to overwrite the cel value with the letter "N" intead of a lookup formula that returned the value "N", but to the unaided eye these are identical.
On a small number--say, 500 or so--I didn't replace the formula with its resulting value.
Generally, that's okay, it'll still read the same, until someone does a sloppy sort on the data. Then, cells on line 80 start referring to cells on line 64, or whatever.
Now, I'm checking through some 600 documents for these maladjusted numbers. This is taking forever...