Dear @eoasker,
What is important is the processing baseline of your product of interest, not necessarly its date of acquisition as the product may have been reprocessed with a newer processing baseline (e.g. Collection-1 products).
Thanks @Marco_EOM for your inputs, the FAQ #4 has been updated with:
Since Processing Baseline (PB) 04.00 (25/01/2022), a radiometric offset has been introduced in order to preserve/provide negative radiometric values.
For these products, please be sure to perform the correct conversion when moving from Digital Number (DN) to Surface Reflectance (SR):
L2A_SR = (L2A_DN + BOA_ADD_OFFSET) / QUANTIFICATION_VALUE
For PB 04.00, 05.00, 05.09, 05.10 & 05.11 the actual values are:
L2A_SR = (L2A_DN - 1000) / 10000
Please refer to the following links (section: Level-2A processing): Processing Baseline - Sentiwiki and Copernicus Dashboard - Processors Releases | ESA