Dan,
I read that document before posting. See, if I follow the documentation as you suggest, then I would want to use non-atmospherically-corrected image for the Tasseled Cap function. Maybe if I calculate NDWI and NDVI, the results might be OK but not optimal. But if I want to do image classification (supervised or object-based) and compare results from different vintage of images, then it's required I use the atmospherically-corrected version.
As backup for my stance, the section on Atmospheric Correction in Imagery and GIS Best Practices for Extracting Information from Imagery (by Green, Congalton & Tukman, ESRI Press 2017 pp 153-156) supports this, and also mentions that "availability of [atmospheric absorption data from specific bands within the image],.... has sparked a resurgence of algorithm development to produce better absolute atmospheric correction methods." (p155). What is not clear is whether the latest capabilities have been programmed into ArcGIS/Pro.
So, might you or anyone have a link to an document that describes the exact parameters used (the formula) in ArcGIS Pro or ArcGIS 10.5, and the methodology followed to derive them? The existing documentation is still a bit of a black box, and doesn't seem to have been updated other than adding newer sensor names. For the public health project I'm supporting on a volunteer (zero pay) basis, this is far less than ideal.
For now, until I get or find more definitive information, I must ignore the Tasseled Cap function because it may give varying results from image collected on different dates because the reflectance will vary along with variations in atmospheric moisture content.