I had a DSL100 and DSL50 back when they were current. I gigged with them alot and used to sing their praises online. They were both from '98 or '99 and the bias drift issue wasn't a known thing yet. I didn't have any problems with them at all. I guess I was lucky?
Just recently, I ran across a '98 DSL50 in great condition that sounded killer. I bought it mostly because I regretted not keeping one when I had them. I've biased it up and left it run for a while, played for a while, etc... and the bias didn't drift. But that wasn't during real hard use, so who knows.
I recorded an all original CD with a DSL50 cranked into a 1960AX cab with Greenbacks and the tone is perfect.