FCL.740.A Revalidation of class and type ratings — aeroplanes
— 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.
So it can be any number of flights totalling one hour with any number of instructors. Logically, the FI signing on the basis of FCL945 would need to be the last instructor conducting the qualifying training.
Each instructor would need to have endorsed the training in accordance with AMC1.FCL.050 b(4)
(4) instruction time: a summary of all time logged by an applicant for a
licence or rating as flight instruction, instrument flight instruction,
instrument ground time, etc., may be logged if certified by the
appropriately rated or authorised instructor from whom it was received;