You can't have an SSEA on a pre-JAR PPL (A) or any JAR or EASA licence.
SSEA was created by the UK CAA to describe the aircraft covered by one of the types of NPPL.
(basically, light aircraft minus microlights)
The problem they were trying to solve was that the old UK PPL (A), the JAP SEP and the EASA SEP all allowed one to fly microlights (albeit with differences training where the control system was different - ie weightshift - to what one's experience had been in).
That's an ICAO problem.
The UK CAA wanted to stop pilots - who were legally allowed to fly microlights - jumping into them and killing themselves. But they could only change UK ie NPPL, non-ICAO compliant licences.
So SEP means light aircraft including microlights, SSEA means light aircraft excluding micros.