How to calculate the radiometric Offset Sentinel 2 L2A before Baseline 0400


I have two questions regarding the handling of the radiometric offset for the Sentinel L2A data in SNAP.

if I activate the option “Add negative radiometric offset” as described in this post ([[INFO] Introduction of additional Radiometric Offset in PB04.00 products]( , what influence does this have on the calculation of the NDVI for L2A data before PB 04.00 and afterwards?
Will the offset be subtracted for all data?

if this is not the case, do I have to manually subtract the offset for data processed before PB 04.00 for bands 4 and 8? And if yes, where and how would I do this?
I hope you can help me with this. Thank you very much.

I cannot answer the first question how SNAP is doing it for older products when you activated the option to handle the radiometric offset.
However, products before PB 4.00 had no radiometric offset respectively it was zero. By the way, you find the information about the radiometric offset and quantification value to be used in the metadata file MTD_MSIL2A.xml in the product folder.

The “Add negative radiometric offset” option is ignored for products before PB04.00

Thanks a lot.