Hi Aleš,
I assume that the sensor that you are referring to his Sentinel-2 and its L2A data collection?
If so, then I can refer you to our documentation here, which explains some of the changes that were made to the dataset in version 4.00. There was also some discussion about this in the Forum that you can read here.
I would also recommend reading through the documentation about the Processing Baselines on ESA’s own website.
Hope that these links help you answer your questions 