When was Simul-class first offered?

[Power&Volume]

Title says it.
Production year and was there model cross over? Late MKII-A into MKII-B?

 

[RobbieAG]

Not sure when the first one was, but I ordered a Mark III with Simul-class around 1985. Too bad the amp was later stolen

 

[DavidMenke]

I ordered Simul Class in around 1984 in an SOB.

 

[woodbutcher65]

The Mark IIB was the first model with available Simul-Class, to the best of what I've been able to discover.