Simple, the 146 family is the first generation of these British built jets. The versions of the 146 are the -100, -200 and the -300. The second generation of the BAC jet is the Avro RJ
series - RJ70, 85, and 100. The third generation since abandoned post 9/11 was to be the Avro RJX70, 85 and 100.
From the outside you'll be hard pressed to find differences between the first and second generations. The Avro RJs have upgraded avionics, engines, pressurization systems, can fly higher and slightly faster and are more efficient. Basically, the same a/c with modern insides. The third generation was to build upon the RJ
family with newer and more poerful engines, even more improved avionics and some other new luxuries.
That's about it...