What were they thinking?

[Go4fun]

So you get some color on your car model and pick out a number (A pair of ten sided dice works well for this.   ) and when you look you find some that fill the bill... for each side. For the roof? Good luck Chuck! I have to wonder if these people making the decals even have a clue about the need for three sets of numbers.

Do any other venue (ships, aircraft, space craft) run into these shortfalls?

[Weaver]

Kinda. You find some aftermarket decal sheets for aircraft give you two or more options for almost every decal for a particular type, except one, so you can almost do two models from the same sheet, but not quite.... frustrating.

[Mossie]

Model Alliance (they're not the only ones) are good for that kind of thing.  They give you a decal sheet with say, ten aircraft markings, but they only give you roundels for one.

[Dizzyfugu]

There are also aftermarket sheets for slot cars in 1:24 and 1:32 scale available - for historic cars, but also generic stuff. Check ebay, and you might find that stuff as specialist stores for die car collectibles, too.