Do you have a reference for this? I must have spent an hour looking an still no joy!
Yes, FCL.740.A Revalidation of class and type ratings – aeroplanes
(b) Revalidation of single-pilot single-engine class ratings.
(1) Single-engine piston aeroplane class ratings and TMG class ratings. For the revalidation of single-pilot single- engine piston aeroplane class ratings or TMG class ratings, the applicants shall:
(i) within the 3 months preceding the expiry date of the rating, pass a proficiency check in the relevant class in accordance with Appendix 9 to this Part with an examiner; or
(ii) within the 12 months preceding the expiry date of the rating, complete 12 hours of flight time in the relevant class, including:
— 6 hours as PIC,
— 12 take-offs and 12 landings, and
— refresher training of at least 1 hour of total flight time with a flight instructor (FI) or a class rating instructor (CRI). Applicants shall be exempted from this refresher training if they have passed a class or type rating proficiency check, skill test or assessment of competence in any other class or type of aeroplane.
No specification of the same instructor or any minimum number of flights!