My understanding is this - that only the in-built tax codes (not custom tax codes) will appear on the tax worksheets due to the fact that when you are creating those custom tax codes there is no option (box) where you can nominate a tax worksheet location / position.
Therefore, for the tax worksheet to be fully functional you can only use the in-built tax codes. The guide should have a “warning” under Custom Codes to that effect.
Therefore the above example is how to handle VAT by using the in-built codes - read these topics.
(NOTE - reference to an import tax code applies to Australia only)