Thank you Marco,
I know it is supper difficult to get this information from ESA but I remember last year i eventually managed to find this piece of information on the ESA website. At that time, the processor used for L2A data was very outdated and I ended up processing L1C to L2A myself. I am not sure whether ESA recalculated the archives since.
I find it interesting though that the internal sen2cor version is 2.8 whereas the one featured on the website now is 2.5.5 [http://step.esa.int/main/third-party-plugins-2/sen2cor/].
lets stay tuned