Car #'s 1,2 and 3 (if used) are given to the previous years manufacturers champion.
example (2013) Audi won the manufacturers title, there for in 2014 they use #'s 1,2. and #3 for a 3rd car at Spa 6H, Le Mans 24H.
Toyota won the title in 2014 so they got #'s 1,2 for 2015, and Audi went back to using #'s 7,8 and #9 (3rd car) for Spa 6H and Le Mans 24h
Car # 7,8,9 seem to end up with the 2nd place team
Car numbers 1 to 49 are for LMP1 and LMP2 and numbers 50 and up are for GTE Pro and GTE Am.
Sevach wrote:
The 17 is a strong favorite anyways, even a 3rd place guarantees the title, without reliability issues they got it.
Both for Porsche #17 and for me remembering the car numbers properly