Spanners
Sorry - I have to disagree. My take on it is that the "approved" assessor is needed to sign block 13 of the application form, not for over-signing worksheets. ELGD A17.1 and A17.2 are the usual shade of greyness that allows interpretation either way and hence could be "debated" either way with the authority.
Another way to look at it, in a medium or large organisation, is it practical to have multiple names listed in the MOE or applying to the authority for approval for the over-signing of worksheets?
Also, if you dig deeper into what is required to be an "approved" assessor, you will find EASA and the CAA contradicting each other and themselves in different documents.