I'm not sure what help you are after. It is what it is.
From Annex VI to Commission Regulation (EU) No 1178/2011 (as amended):
ARA.FCL.215 Validity period
(a) [..]
(b) [..]
(c) The competent authority, or an examiner specifically authorised for that purpose by the competent authority, shall enter the expiry date on the licence or the certificate.
(d) [..]
Was/is your Dutch examiner "specifically authorised for that purpose by the competent authority" i.e. in this case, the UK CAA? Assuming that he was/is not, then, in my opinion, the CAA is technically correct, as frustrating and nonsensical as it may seem.