Ok, I'll tell you exactly what a Level/B'Day ticket is.
Say you've just got a Level 24 ticket. Theres only 3 cars that are Level 24 namely F10, F2007 & FGT. You preceed to open it. You'll either get one of the 3 cars. Got it?
A B'Day ticket is completely different.
Its your Birthday and you go on GT5. Say your Birthday is in 1980, the game (So long as you're signed in to PSN) will give you a 1980 ticket. This means you could have ANY car out of that year.
Also theres a Ticket 1000.
Say you've just taken to the track 100 times or driven 2000km (in A-Spec), the game will offer you a Ticket 1000. You could get any car in the game out of this Ticket (Excluding the Red Bull X1) so its just a matter of luck that you get the car you want, same with every other Ticket really.