In Europe, helicopters are heavily type-oriented, so each helicopter you fly is held on your licence as a different type rating (broadly speaking - there is the odd exception). Each year you must revalidate the type ratings you hold:
FCL.740.H Revalidation of type ratings – helicopter
(a) Revalidation. For revalidation of type ratings for helicopters, the applicant shall:
(1) pass a proficiency check in accordance with Appendix 9 to Part-FCL in the
relevant type of helicopter or an FSTD representing that type within the
3 months immediately preceding the expiry date of the rating; and
(2) complete at least 2 hours as a pilot of the relevant helicopter type within the validity period of the rating. The duration of the proficiency check may be
counted towards the 2 hours.
(3) When applicants hold more than 1 type rating for single-engine piston
helicopters, they may achieve revalidation of all the relevant type ratings by
completing the proficiency check in only 1 of the relevant types held, provided that they have completed at least 2 hours of flight time as PIC on the other types during the validity period.
The proficiency check shall be performed each time on a different type.
(4) When applicants hold more than 1 type rating for single-engine turbine
helicopters with a maximum certificated take-off mass up to 3175 kg, they
may achieve revalidation of all the relevant type ratings by completing the
proficiency check in only 1 of the relevant types held, provided that they have completed:
(i) 300 hours as PIC on helicopters;
(ii) 15 hours on each of the types held; and
(iii) at least 2 hours of PIC flight time on each of the other types during the
validity period.
The proficiency check shall be performed each time on a different type.