You're right mate, teams did field more than two cars in a team. But this was mostly back around the 1950s and 60s. The British GP in 1955 for example, Mercedes Benz finished 1-2-3-4 Back then there wasn't really a limit on how many cars you could run. But also, for example, say you wanted to go racing, but couldn't afford to build your own car from scratch, back then you could strike a deal with say Lotus, and run a customer car in your name and go racing that way.
It's from the 70s onwards where it eventually became structured and all round cheaper to field two cars per team.
And before a certain female member says I only know this because I'm old and apparently from those days I'm really into the history of the sport.