A synthesis of the error budget estimated for the whole ESA Envisat Altimetry Full Mission Reprocessing level 2 products can be found in the Error Budget of Envisat Altimetry MIssion. This takes into account the homogeneous reprocessed v3 data set, achieved in March 2018.
Altimeter v3 dataset Verfication documents
Altimeter v2.1 dataset Verfication documents
Envisat RA2 GDR Quality Assessment