The 6 sittings is a new EASA FCL.025 requirement.
FCL-025 (3) If an applicant has failed to pass one of the examination papers within 4 attempts, or has failed to pass all papers within either 6 sittings or the period mentioned in paragraph (2), he/she shall re-take the complete set of examination papers.
The CAA now propose 9 examination papers. They don't however seem too concerned about this requirement:
AMC1 FCL.215; FCL.235
THEORETICAL KNOWLEDGE EXAMINATION AND SKILL TEST FOR THE PPL
(a) Theoretical knowledge examination
(1) The examinations should comprise a total of 120 multiple-choice questions covering all the subjects.
So much for "STANDARDISATION"! The RT practical appears to remain separate and presumably, is not considered in the term "all"!
Stds Doc 11 V10 was only issued in October and in less than 2 months has had to be replaced with V11! Is it any wonder that nobody can keep up.
The CAA never mastered the administration of F252s so what chance for the 2155 especially as many PPL students do not have a reference number!
Reading Doc 11 para 2.12.6 it states that a candidate who fails the 4th paper will have to resit all PPL Exams at Gatwick or a CAA Exam Centre. They do not appear to have invented a form for this one yet. SRG 2165 only caters for the 4th attempt. The cost of the resit £350 for 7 papers or £450 when they go to 9 papers. Will an ATO want to administer this process as they won't derive any income from it, will it be left to the candidate or will the CAA administer it until completion?