I reckon that would apply to mainstream watches only and custom dials for customers would be however many the customer wanted, provided they were willing to take the cost. I imagine service dials often go by the by when negotiations are going on, it's not the first concern of either Heuer or the customer. Of course, the end customer might end up with a messed up dial they can't replace but that's later down the line - I'd be willing to bet we have lost a few of these to redials and/or dial replacements with standard dials.

I do doubt that any of them only stretched to 4 examples, the costs would probably be prohibitive but, if they really wanted just 4 and were willing to pay, I doubt Heuer (or any watch manufacturer pretty much - I'm sure I've seen promotional dials on Rolexes, maybe a house like Patek Philippe hasn't done it) would turn the business down. These sort of watches probably remain obscured in private collections a lot of the time.