rvwise:

Cessna 135 or 145? Never heard of such numbers. Doesn't mean they don't exist, just that I've never known such model numbrs.

Do you mean a 120 or 140? The only difference in those two was flaps on the 140.

And the only --5 i know of is the 195, the later version of the 190.

Generally, on piston planes, Cessna had the first digit for engine count, second for base model, third number for variant of the base model. An example would be the 172 - 1 engine, 7 series, and 2 indicated the tricycle variant of the taildragger 170. Of course they blew it with the twins. First digit was 3 for them. The 310 and 377 are two examples.

I'm sure they have run out of numbers in this system so I can't speak with authority for anything in the last 20 years or so. Just like Boeing has only two planes to go in the 7x7 series.

Bill.