My apologies Greg. I'd made my earlier example simpler and forgot to amend on my second post.

I seem to have caused quite a fuss with this post! I dunno if am asking the impossible or just being incredibly bad at wording what I am trying to achieve!!!!?!?!??

In the least confusing sentence possible:

I want to display, on screen only, all parts with the description 'S/A of PCB'. Be it in the top level of the BOM or anywhere 'underneath' that level, given the example extract from the system I am using.

In response to the comments regarding how often the Bill of Materials change, unfortunately, we operate on quite a regular bespoke set of BOMs. I extract the information each week to enable planning of PCB build. Headache I know, but that's the business. 🙁