Neither can I find any reference to it in an old version of LASORS. Can anybody point me to a relevant clause in anything official?
LASORS is well out of date, it is superceded by CAP804 which itself quotes from Part-FCL in respect of EASA Licensing:
Part-FCL Page 9
FCL.010 Definitions
‘Renewal’ (of, e.g. a rating or certificate) means the administrative action taken after a rating or certificate has lapsed for the purpose of renewing the privileges of the rating or certificate for a further specified period consequent upon the fulfilment of specified requirements.
‘Revalidation’ (of, e.g. a rating or certificate) means the administrative action taken within the period of validity of a rating or certificate which allows the holder to continue to exercise the privileges of a rating or certificate for a further specified period consequent upon the fulfilment of specified requirements.
Many people use the terms "Renewal' and 'Revalidation' interchangeably - this is wrong as they have specific, different meanings.
the revalidation (by experience) endorsement must be made prior to expiry
Although we know what you mean, this sentence is wrong.
It should be: "Revalidation (of a Rating) must be made prior to expiry"
- Doesn't matter how the requirements were met
- A revalidation is not 'endorsed'. It is the (administrative) action of an Examiner a) Filling out the line in your Ratings' section, b) Completing the required form and c) Sending the form to the CAA
that is the Revalidation.
NB: I know MJ used the term "endorsed" first, and most pilots don't care about the forms as Examiners usually take care of these (as they are required to do).