Sorry I don't know - I just know that the Luc Lak beef is from the official recipe book. I just try and stick to the rules however changeable they seem to be.
The recipe only has 1 tbspn of oyster sauce and that is to serve 4, but I try not to eat all the sauce if I make it as it is sweet.
Personally I feel that once I start to question why different ingredients are not allowed / on the tolerated list, then I am going to start letting things slip, thinking that a little bit of this that or the other won't hurt. I guess it all comes down to personal choice in the end if you want to start slipping in extras at this stage.