Vlook up not capturing all numbers

Hello - this one just has me stumped and it has to be simple.

I have a workbook with 2 sheets

Main Sheet
School Codes

I'm just trying to do a basic Vlookup to compaire the two sheets.

The Issue = Numbers are in Column A on both Tabs but the Vlook up is still returning #N/A for the last 20 or so.

I've attached an example with PII removed so please point out my stupidity.

thanks.