Is the reg talking about a class rating or type rating? If it's a class rating (which is the case now for most GA aircraft) the pilot only needs to have the class rating in the licence and be satisfied that he/she is confident that they are competitent on the aircraft. Type ratings require specific training on the particular aircraft type.
Example would be that if a pilot had a class rating on a multi engine piston twin, and say had a lot of time in a PA31 and then wanted to fly say a PA34, the pilot could legally fly in the PA34 provided that the pilot was satisfied that he/she were competent enough to fly the PA34. How that competentcy is achieved is up to the pilot/operator to determine. Reading the POH and doing a flight with another pilot experienced on the aircraft might be all that is required, and that other pilot does not have to be an instructor.
I can't see how a syndicate would be drawn into this, they don't hold AOCs.