An ELP is required for a Pilot's Licence, not an FRTOL
From CAP804:
Such proficiency is required, in ENGLISH, for the issue of a UK FRTOL. Where a pilot accepts the limitation of flying non-radio only, or the pilot is the holder of a sailplane or balloon licence, Part-FCL does not require language proficiency to be demonstrated; but it is always required for a UK FRTOL to be valid.
and
To use a FRTOL the holder must have English language proficiency Level 6, or non-expired English language proficiency at Level 4 or 5
For some reason the ELP is ensorsed on the pilot licence, but it's based on the FRTOL. A pilot without an FRTOL cannot have ELP:
Holders of UK issued pilot licences that do not include a Flight Radio Telephone Operators Licence (FRTOL) have no privileges to use radiotelephony for airborne communication, and thus their licences cannot be endorsed with the ICAO Language Proficiency endorsement.
why do people assume an FRTOL is valid for 10 Years
A JAR FRTOL had 10 years validity, unless it was issued at the
same time as a licence - in which case it had 5 years validity. A couple of people I know had 10 years validity (one stand-alone, and one who obtained a PPL after getting a stand-alone FRTOL). It's incorrect to assume that all JAR FRTOLs had 5 years validity (even if you had a PPL).
e) Other Acceptable Means
If the CAA expected revalidation by experience to be covered by Other Acceptable Means, then I would have expected:
a) The list of suggestions of what the CAA consider to be acceptable that are under that section to include examiner face-to-face assessments (it didn't).
a) SRG1199 (issue 01) Opportunities for Assessment section to include revalidation by experience (it didn't).
b) The CAA's statement in 2012 to include revalidation by experience (it didn't):
Since 2008 many UK pilots have been upgraded to Level 6 by demonstration to an examiner during a flying skill test, a proficiency check or a radio licence practical test. However, there are believed to be a significant number of pilots, mainly in the general aviation community, who have not obtained a Level 6 assessment from an examiner within the last four years during a test or check.
That doesn't mean that examiners who did face-to-face assessments were wrong to, and the CAA clearly accepted them. But it explains why some examiners didn't - they were likely following the guidance and SRG1199 instructions. Clearly the CAA didn't realise that many pilots revalidate by experience when they produced the ELP guidance and paperwork.