Yes, the T12 series came after the Slimstar series.
The chassis are totally different:
The Slimstar have an enamel tank and the body is fully removable so you have a perfect access for servicing.
The T12 have a plastic tank and you can just remove the right plate for servicing (it's somewhat hard to replace the drain pump or the left drum bearing).
The early T12 (with DC PM motor) had spin-drain but at 120rpm instead of 200rpm, the later ones (with universal motor) had a Ceset motor with tachometer for speed regulation and some cheaper models had an asynchronous motor (spin speed 400 or 500rpm).