With the new system. It can be very difficult to elongate your basic training.
1A completed in unit 2x Weekends.
1B at an RTC 4x Weekends(Usually).
You then have eight weeks to attend your 2 week 1C course before you require revalidation from the 1B RTC. After 6 months from your 1B course then you will be required to re-attend the full 1B again.
Quite a few repeat 1B for a variety of reasons, usually missed weekends through work commitments.
Each unit should be able to answer your questions. Or at least know someone else that can answer them correctly.