Things like ABS, driver's airbag, rear headrests, factory alarm, power front headrests, memory seats and central locking actuation from passenger side and trunk were added as stadard equipment or options over time. Maybe orthopedic seats as well.

I prioritize condition and color combo over a particular year, myself. I'm turned off by the added complexity of an 85, but I wouldn't dismiss it. If you're used to cars with all around central locking, you might lock the trunk and leave unattended your unlocked early SD.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD