Back in the day, when I worked at McD's - this was quite a while back as we had to use actual arithmetic to add up all the prices, look up the tax on a table (usually memorized) add that in and then count out the change to each customer, figuring in the exchange rate if the customer was paying in Canadian dollars - phew, that was long segue! Anyway, at that time there was no lettuce or tomato on the fish sandwiches. Clearly, that was long, long ago 
and very far away from where I live now but I've never been served any since at any of the airport locations I've visited. Of course individual franchisees always had a certain amount of flexibility to modify.
Back in those dark ages, we always used 1/2 a slice of cheese on each fish sandwich but because of the way the cheese slices broke, it was usually more like 1/3 on some and 2/3 on others.
The tartar sauce was dispensed in the same sort of "caulking gun" (remember we're talking way back) as the Big Mac sauce but it was chunkier so the amounts dispensed tended to be more random. The randomness of tartar sauce delivery seems to continue to this day.
Edited to add that I restrict my McD's to airports and even then only with significant delays but this is making me want one of their fish sandwiches. And it's not even Lent!
