Hi, I think you need to step back a level.
If you haven't done so already, you should familiarise yourself with EN 50581, which will cost Euro8 from https://www.evs.ee/products/evs-en-50581-2012
As a manufacturer you should assess your suppliers and the parts that they provide on the basis of the risk of the product and the trustworthiness of the supplier and the relationship you have with them.
You are required to do "due diligence".
For some combinations of products and suppliers that might be "CoC with every order and random samples submitted for analysis" or it might be "DoC from supplier and RoHS status checked on website or specified on PO"
There is no right or wrong answer, and if there is any additional work involved beyond supplying a copy of a Declaration of Conformity, the cost will be borne by someone....