Article 9 of document 843 says "Certificates of airworthiness, certificates of competency and licences issued or rendered valid by the United Kingdom and still in force shall be recognised as valid by the Member States for the purpose of the operation of air transport services by UK air carriers under this Regulation, provided that such certificates or licences were issued or rendered valid pursuant to, and in conformity with, as a minimum, the relevant international standards established under the Convention." Which, from the point of view of flight crew licenses only says to me that UK issued licenses, ratings etc., will be accepted as valid when operating for UK carriers in the EU.
Document 844 does not relate to flight crew licensing, as you say, apart from Article 5 which says: "By way of derogation from Commission Regulation (EU) No 1178/20119 and Commission Regulation (EU) No 1321/201410, the competent authorities of the Member States or the Agency, as the case may be, shall take account of the examinations taken in training organisations subject to oversight by the competent authority of the United Kingdom prior to the date of application referred to in the second sub-paragraph of Article 10(2) of this Regulation, as if they had been taken with a training organisation subject to the oversight of the competent authority of a Member State." I'm not sure what this means, nor what the "examinations taken in training organisations" could possibly be.