Gdcprogrc wrote...
For example
=SUM(INDIRECT(C10))
where C10 would contain
="Sheet2:"&"Sheet3!"&"A"&ROW()
always returns #REF!.
....

No. INDIRECT can only return range references. 3D references are never
range references.

You could use a list of worksheet names, e.g., WSLST referring to

={"Sheet2","Sheet3"}

then use the formula

=SUMPRODUCT(N(INDIRECT("'"&WSLST&"'!A"&ROW()))