On most equipment the numbers will be a size within a series of machine. (example, John Deere the last 2 numbers are the series xx10,xx20,xx30/ the first 2 numbers are the size 62xx,63xx,64xx) So a 6210 is the same size as a 6230 only older while a 6430 is larger than a 6230. Now if that is not confusing enough the numbers mean nothing more than when chevrolet of Ford puts a name like mustang or impalla on the side of a car. A 6430 is neither 64 or 30 HP. I sell them and still have to look at the book. Just a side note be sure you look at the same type of HP when looking at tractors, Being in the ag buisness we have ALWAYS used PTO HP as the actual number.
Now with all the smaller brands trying to gain market they began using engine HP (this will be much larger). Now all mfg are publishing both numbers so compare apples to apples. If you have any doubts just look up the nebrsaka test, it is the standard by which all tractors are rated not just some number a mfg pluckes out of the air.