VLOOKUP partial match not playing the game

Hi All

I'm trying to get VLOOKUP to work using a partial match on a cell that contains two values seperated by a / eg. 12345/54321 but the results are not correct. The VLOOKUP function works if I enter a value from a cell that has just a single number but not from cell that has the two numbers.

Attached spreadsheet shows the issue

In the example on Sheet Test Data I need to be able to get VLOOKUP to work on Row 18

Any help appreciated thanks