Google-sheets – Attempting to use a LOOKUP with an Importrange tab on Google Sheets to make sure values across two sheets are correct, but I keep getting errors

This is the sheet I am working on. The trouble starts on the tab titled "Sectors and subsectors", on row 56 under the column named "checksum".

What I am attempting to do is as follows. The checksum row is supposed to return the human population in the sector whose name is listed in the column "Sector name". This is to make sure that all of the corresponding subsectors (listed in the column titled "Subsector name") for that sector have a population that sums up to the population of the sector they are in, with the task of subtraction done in the column titled "diminution".

I placed a lookup function in order to find the corresponding values for human population and sector names on the sheet named "Sector list", which is an importrange of the tab "Sectors" on this spreadsheet.

All the subsectors which have the sector name Five were intended to have the lookup formula under the column named "checksum" do the following:

looks up the sector on "Sector list" with an identical value for its name as the Sector name column on "Sectors and subsectors"

looks up the value for human population on "Sector list" in the same row as the sector, and return it

For the preceding ten rows in the checksum column the basic Lookup function worked. However, for rows 56-65, it returned the #N/A error "Did not find value "Five" in lookup evaluation".

…When it's clearly there.

I attempted to use VLOOKUP next. That has the #REF! error "VLOOKUP evaluates to an out of bounds range".

Any help in sorting this out is greatly appreciated.