This is an exemption to allow a 'not properly licensed' pilot to fly UK Registered Aircraft in the UK.
When it was first promulgated the CAA stated it was to remove the admin (& fee) of applying for an NPPL & SSEA Rating for those pilots who wished to continue flying but were
temporarily not fit for Class 1/2.
We may not agree with it but It is, therefore, understandable that the CAA put a time limit on this exemption.
A bit unlucky for those who were only temporarily unfit for 6 weeks in month 23 of their SEP validity, compared to those who were temporarily unfit for 7 months from month 11 to month 18 of their SEP validity.
However, the CAA did, and have, cocked up in the way they have worded the Explanatory Note. They have confused Revalidation requirements with the Exemption requirements.
The ANO did not, and does not, require a valid medical to be held to revalidate or renew a Rating held on a UK National Licence, nor does EASA (which the CAA cannot overrule) require it for Ratings on Part-FCL Licences.
In this exemption a specified pilot licence is a pilot licence issued by the CAA, other than a National Private Pilot’s Licence (Aeroplanes) or a licence issued or deemed to have been issued in accordance with the Aircrew Regulation,
‘Aircrew Regulation’ means Commission Regulation (EU) No 1178/2011 of 3 November 2011 as amended by Commission Regulation (EU) No 290/2012 of 30 March 2012;
Exactly how is the UK CAA going to tell the German CAA (for example) that they cannot revalidate a Rating on a German issued Part-FCL Licence just because the pilot has obtained a UK NPPL Med Dec.
The Explanatory Note should have said something like:
This exemption may be relied upon from the date a pilot first falls below Class 2 Medical standards until the earlier of either:
a) A valid Class 2 (or Class 1) medical is regained
or
b) The expiry date of the SEP Rating which was held at the time that this exemption was first relied upon.
Basically, it is down to the pilot to know they can no longer rely on the exemption - not for an Examiner (or now Instructor) to refuse to action a revalidation request.