Morning again folks.
Yesterday I'd posted a question regarding looking up and comparing data
between two worksheets, and placement of a marker in a tertiary column. Roger
Govier, and Pete_UK graciously responded, and had provided an answer to my
questions.
They provided the following nested functions, with my modifications now
included.
The first is Roger's
=IF(E5="","",INDEX(SUMMARY!$B$10:$B$60,MATCH(E5,SU MMARY!$A$10:$A$60,0)))

And these are Pete's
=IF(ISNA(MATCH(E5,SUMMARY!$A$10:$A$60,0)),"",INDEX (SUMMARY!$B$10:$B82,MATCH(E5,SUMMARY!$A$10:$A$60,0 )))

=IF(ISNA(MATCH(E5,SUMMARY!$A$10:$A$60,0)),"",VLOOK UP(E5,SUMMARY!$A$10:$B$60,2,0))

I've saved these in a notepad file so I have them at the ready for my use.
At first, all three of these worked. All three provided the same exact
answers when placed side by side.

Later on in the day-- yesterday afternoon, and again this morning, I set
each of them in a different worksheet, modified the column, and row values.
Roger's now leaves me with the #N/A error, and Pete's leave the column blank
with no corresponding letters.
I've gone through and made sure that my row upper and lower limits are
correct, that my columns, and other elements are all accurate-- double, and
triple checking myself-- and I keep getting the identical response-- #N/A, or
blanks (where letter values should be).

My questions a
1- the most obvious.... what's wrong.
2- are there certain conditions beyond the obvious (columns, rows) that are
required for this configuration of nested functions to work? I.e., they all
worked in one file, and now don't work in the remainder of my files (three
that I've tried since the first yesterday morning).
3-I just went back, used Roger's original equation, selected the correct
columns, placed absolute references B$9:..... to make sure that when I drag
it down the top, and bottom limits aren't skewed. I'm still receiving the
#N/A error.

Your helps are appreciated.
Best.