Thinkpad duplicates?

[Thinkpad4by3]

Seems that Thinkpads had models that were in the same machine in two different numbers. Why?

So far I have come up with this:
Thinkpad 755C and 370C
Thinkpad 355C and 360C
Thinkpad 240Z and i1142
Thinkpad 380 and 385(all machines)

[madicetea]

Seems that Thinkpads had models that were in the same machine in two different numbers. Why?

So far I have come up with this:
Thinkpad 755C and 370C
Thinkpad 355C and 360C
Thinkpad 240Z and i1142
Thinkpad 380 and 385(all machines)

I'll try to do some research on point 3, but it might be the weekend before I get back with any findings, so I'd like to know if anyone figures it out before then.