A plug-in can have any number of parameter blocks. All the parameter blocks for that plug-in should be associated with the same class descriptor. This is accomplished by passing the same class descriptor object address to each parameter block descriptor constructor. For example:

static  ParamBlockDesc2 widget_param_blk (
   //...
   , &WidgetDesc,
   //...
);
 
static  ParamBlockDesc2 widget_param_blk_extra (
   //...
   , &WidgetDesc,
   //...
);

When 3ds Max creates the parameter block by calling ClassDesc2::MakeAutoParamBlocks() it automatically loops through all the parameter block descriptors that have been registered with the class descriptor.