How many times did Rastapopoulos and Haddock meet?

I could count only one: Flight 714. Had they ever met, face to face, before?

Now that you mention it, they might have seen each other from a distance but never face to face before Flight 714. Although not part of the core series, they also had a face to face meeting in the Lake of Sharks.

In "Red Sea Sharks" and "Flight 714", Haddock is more focused on his personal vendetta with Alan, Rastapopoulos's henchman. They have old scores from "Crab" when Alan tricked him by using his ship to smuggle drugs - among other things.

To each his own enemy.

Flight 714 is the first meeting between the two some 12 books after the introduction of Captain Haddock.
I not sure if we can include lake of Sharks into this but I dont see why not.