Genghis,
You are absolutely right that the seaplane class ratings are listed in some states JAR-FCL-licences. This listing can create some confusion, as the two sea class ratings belong to the group of national ratings that
may be entered into JAR-FCL-licences, just as a few other national ratings of various kinds may.
You'll find the reference in JAR-FCL 1.215 (c) (1), Subpart F, page 1-F-1.
(c) The requirements for the issue, the revalidation, renewal for the following class ratings are at the discretion of the Authority:
This implies that JAA recognizes the
existence of seaplane ratings, but has not done one iota of standardisation or harmonisation work on seaplane ratings, neither the syllabus, the contents of the Skill Test, the revalidation requirements, nor the contents of the ProfCheck - if the state chooses to require one, with the resultant lack of mutual recognition. No JAA state is obliged to accept any such national rating (Albeit some states choose to do so)
Cheers,