First of all, 3.5.4 is the requirement for intermediate process steps that done by your subcontractor. Therefore, if your subcontractor did all process and submit to your buyer directly, the requirement will not applicable to your company. For example, your company produces fruits (as frozen or juice or canned or dried). You buys fruits as whole fruit from your suppliers, then subcontracts external company to help the raw material preparation section to peel some quantities of the fruit before returning the peeled fruit back to your company to process as final products together with the one prepared by the raw material preparation section. Your fruit supplier is under 3.5.2 while your peeling subcontractor is under 3.5.4. Therefore, you need to have procedure to approve and accept whole fruits as well as peeled fruits.
For 18.104.22.168, there are 3 choices for you to monitor these outsourced processing: 1) audit by your company, 2) they certified GSFS, 3) they certified other GFSI standards.
Hope my answer can help.