I think A and B have to do with the type of motor (1-phase vs 3-phase?)
And T denotes dual tone. So Thunderbolt 1000 is single tone and Thunderbolt 1000T is dual tone. The 1003 doesn't need the T because it only comes in dual tone.
There's a possibility that it might've been refurbished before in its lifetime. Then again, it's probably shielded from the sun by all the trees.