I read, am afraid can't provide a reference at the moment, that LPC an is good for 12 months, you get 3 months 'grace' to renew without penalty. After that and before 3 years you need 'additional' training. I can't define 'additional' in this context. After 3 years as stated complete type rating, and 7 (6) years do the exams.
I suspect there will be a new lease of life for the Seneca's dotted around the UK as I think the cheapest way will be a MEP class rating and IR to avoid re-sitting the exams and a ride with CAAFU.