*many quotes*
I'm somewhat of a Focus nut so I've looked into quite a lot of Focus keyboards. Here's the generations I've divided them into so far:
0th gen (we don't know exactly when these were, just that they were before the others):
555, 747
1st gen:
1001, 2000plus, 2001, 2002, 3001, 5001
2nd gen:
6000, 7000P, 8000, 9000
3rd gen:
6200, 7200, 8200, 9200
Rough succession line:
2001 -> 6000 -> 6200
2001 -> 2001 -> 2001
7000P -> 7200
5001 -> 9000 -> 9200
0th gen are all blue Alps and occasionally cyan Omnoms. 1st gen were originally blue Alps but went through to white Alps which most of them are. 2nd gen came with white Alps originally but after that clones and even occasionally completely different switch types like Futabas. 3rd gen are Focus dome with slider. The FK-2001 appears to have transcended way past its own generation and bled into the 2nd and probably even the 3rd generation, probably as a "classic" model, a bit like Unicomp's Ultra Classic Model M which runs alongside their current one. By that time it had gone from a 101-key AT/XT keyboard with genuine Alps switches, doubleshot keycaps and a built-in dust cover to a 104-key PS/2 keyboard with some fairly vile clones, partially pad-printed keycaps and they left out the dust cover as well - a major decline of such an awesome keyboard.
Of course there are many gaps in my knowledge as well, but this is what I've found so far. The one who knows most about Focus is probably Engicoder, he has even more than I do xD .