oh, and:

-no numbers between 822 and 901
(because VW wanted align Porsche numbers with its own, 900 series was the only one left or VW)

from 1963 on:
-numbers 900 until 1000 was reserved only for Porsche projects.
-1764 until 3512 was for outside/foreign firms research contracts.

- Elva Porsche: no number
- Lotus Porsche: no number
- 16cyl motor of Piech (1971) destined for Can-Am series does
not have number (apparently for hiding development)