Sorry Beagle I can't understand your last post.
Well I'll try and make it simple...
First of all, remember that this is an EASA regulation for all MS, not just for NPPL(SSEA) holders...
Let's say that an NPPL(SSEA) holder has only flown the 10 hrs PIC required for the NPPL to have been issued in the first place. The DTO does an assessment and decides that, although he/she could have been granted 10 hrs credit, his/her flying isn't all that good, so they'll only grant 7 hours of credit.
Before taking the LAPL(A) Skill Test, the applicant will need to do the 15 hrs of dual training and 6 hrs (including X-C requirements) PIC plus whatever flight time hasn't been credited by the DTO. In the case I've stated, 7(credit)+15+6 = 28 hours, so the applicant will also need to fly a further 2 hours (which can either be dual or solo), before he/she may take the Skill Test.
If the NPPL exams were passed in the 2 years before the LAPL Skill Test, then as far as I can see they will be valid for LAPL application. More than 2 years and they'll have to be retaken.
Why on earth anyone bothered with an NPPL(SSEA) course after 8 Apr 2018 is rather beyond me - they should have transferred to a LAPL course. Of course an NPPL(Microlight) holder might have added an SSEA Class Rating after 8 Apr 2018, but should have been advised that after 8 Apr 2020, the NPPL will not be valid for flying EASA aircraft under current regulations.