If the vendor creates a property for each plot in the property section, the plots should be accessible.

As an example you can have a look at the MACD. In the properties section of the code, there are three public DataSeries Default, Avg & Diff. These public DataSeries allow to access the 3 plots.

If your vendor has forgotten to create such public DataSeries objects, the plots cannot be accessed.

If you have an indicator with a single plot (not other plots), such as the EMA, it is not necessary to declare the public properties, as you can directly access the indicator.

Harry

You also can access value for Plots without public DataSeries defined.
There is public DataSeries[] Values from IndicatorBase which you can access.
Values[0] are values for Plot[0], Values[1] are values for Plot[1] ...