"Jamie's NSR Homepage" has an excellent quick reference guide of the different models and their livery's here. And a more detailed listing here.
NSR250.net has an excellent history of model development here.
NSR-World has a very good history of the model development here.
Honda motorcycle press releases are all here.
Some of the basic differences between the models
* implies SP model
The SP's have dry clutches, Magtek rims, and more adjustment in the suspension (except MC18 4j which has same suspension).
The SE's have dry clutches, Enkei aluminium rims and more adjustment in the suspension. SE's exist for MC21 and MC28 only.