Paco,
FCL.025 reads
(c) Validity period
(1) The successful completion of the theoretical knowledge examinations will be valid:
(i) for the issue of a light aircraft pilot licence, a private pilot licence, a sailplane pilot licence or a balloon pilot licence, for a period of 24 months;
(ii) for the issue of a commercial pilot licence, instrument rating (IR) or en route instrument rating (EIR), for a period of 36 months;
(iii) the periods in (i) and (ii) shall be counted from the day when the pilot successfully completes the theoretical knowledge examination, in accordance with (b)(2).
(2) The completion of the airline transport pilot licence (ATPL) theoretical knowledge examinations will remain valid for the issue of an ATPL for a period of 7 years from the last validity date of:
(i) an IR entered in the licence; or
(ii) in the case of helicopters, a helicopter’s type rating entered in that licence.
So although he could get his IR issued on a PPL, the theoretical exams for his CPL will have run out so he would have to redo the exams to get a CPL.