Substituting a calculated range into a lookup - excel

Question

In the contents of cell F3 I have the following formula (which takes one value on the current row and looks it up in another sheet, returning a range based upon where it was found):
="'OBS Procedures'!" & ADDRESS(MATCH(INDIRECT(ADDRESS(ROW(),1)),'OBS Procedures'!A:A,0),3) & ":" & ADDRESS(MATCH(INDIRECT(ADDRESS(ROW(),1)),'OBS Procedures'!A:A,0),50)
which outputs, as it ought, the text : 'OBS Procedures'!$C$1:$AX$1
All good so far.
I have in another cell (which outputs the rightmost filled cell of the range generated by cell F3):
=LOOKUP(2,1/(INDIRECT(F3)<>""),INDIRECT(F3))
And this outputs , as it ought, the text : 5 : 18/07/2016
Great.
But I'm wanting to get rid of cell F3 entirely, and incorporate the formula for F3 into the second formula above.
Simply copying in the F3 formula between the second INDIRECT() works fine. But copying it into the first F3 generates #N/A.
Specifically :
=LOOKUP(2,1/(INDIRECT("'OBS Procedures'!" & ADDRESS(MATCH(INDIRECT(ADDRESS(ROW(),1)),'OBS Procedures'!A:A,0),3) & ":" & ADDRESS(MATCH(INDIRECT(ADDRESS(ROW(),1)),'OBS Procedures'!A:A,0),50))<>""),INDIRECT(F3))
generates #N/A
Whereas even
=LOOKUP(2,1/(INDIRECT("'OBS Procedures'!$C$1:$AX$1")<>""),INDIRECT(F3))
and generates what I expect
(Keeping the intermediate cell or doing this in VBA, which is my usual go-to for anything more than simple formulae, isn't an option in this case)
I'm simply not seeing what I am doing wrong here - can anyone enlighten me, please? :)

Answer 1

As hinted at in my comments, I'm afraid to say that the construction you are currently using is a very poor one indeed, and could be replaced with a set-up which is both non-volatile and far more efficient.
The reason for your error is due to the manner in which you are using the ROW function. In fact, for generating incremental integers in this manner, ROW is, for several reasons, inferior to ROWS (https://excelxor.com/2014/08/25/row-vs-rows-for-consecutive-integer-generation/).
Despite its inferiority in this respect, however, this does not usually lead to errors. Here, you are a little unfortunate in that, due to the nature of your construction, Excel is expecting an array output from the portion:
ROW()
As such, and assuming for the sake of argument that the formula we are discussing is in row 1, this part:
ADDRESS(ROW(),1)
which, under different circumstances, would evaluate to:
"$A$1"
here evaluates instead to:
{"$A$1"}
since the LOOKUP is lending the necessary array-coercion to the overall construction such that the ROW() portion is expected to deliver an array output, albeit one containing just a single value. In fact, here (and you can see this by using the Evaluate Formula feature), this part evaluates to (for row 1), not 1, but {1}.
And so here:
INDIRECT(ADDRESS(ROW(),1))
is:
INDIRECT({"$A$1"})
and since, in general, INDIRECT is incapable of resolving an array of values (though this can be achieved via further manipulation), this part errors.
To avoid this, you can use ROWS, e.g. (for row 1):
ADDRESS(ROWS($1:1),1)
or else coerce the array output from ROW into a non-array type via some suitable additional function, e.g. SUM, viz:
ADDRESS(SUM(ROW()),1)
That said, I really think that you need to rethink your whole approach here. For example, this:
=LOOKUP(2,1/(INDEX('OBS Procedures'!$C:$AX,MATCH(A1,'OBS Procedures'!A:A,0),)<>""),INDEX('OBS Procedures'!$C:$AX,MATCH(A1,'OBS Procedures'!A:A,0),))
assumed to be in row 1, would be equivalent to your:
=LOOKUP(2,1/(INDIRECT("'OBS Procedures'!" & ADDRESS(MATCH(INDIRECT(ADDRESS(ROW(),1)),'OBS Procedures'!A:A,0),3) & ":" & ADDRESS(MATCH(INDIRECT(ADDRESS(ROW(),1)),'OBS Procedures'!A:A,0),50))<>""),INDIRECT(F3))
(again assumed to be in row 1), and not only does not require the prior construction of a text string representing a range, but is also concise and, importantly, non-volatile.
Regards