Hello

I just started using Sentinel 2 data for exploring changes in tree vitality for certain areas in Germany.
Using Copernicus Browser to search for images I realized that, especially for newer images, two different datasets per image are offered e.g.:

S2A_MSIL1C_20210910T101031_N0500_R022_T33UUU_20230116T100413.SAFE
S2A_MSIL1C_20210910T101031_N0301_R022_T33UUU_20210910T122319.SAFE

When I calculate NDVI for the images I get quite different results, about 0.2 to 0.25 units lower when I use the first dataset.

Can someone tell me for what the second date and the changing N… values in the naming of the datasets stand for?
I guess it has something to do with the preprocessing of the images.
Another question would then be what do I have to take into account when comparing images from 2017 with images from 2021 and 2023 or rather where can I get further information about that?

Thanks for you help in advance.

Best