Since the SGDRs contain the waveforms, the high rate information can also be included. That's why the 20hz signal is included.
Jason-2 is currently in a geodetic orbit, so it depends on when you are getting the data. If it is in the nominal orbit, the current one Jason-3 is in then you should be seeing similar errors. If you are trying to use Jason-2 data October 2016 or later, that will be the geodetic orbit and the errors will be greater.
PO.DAAC Data Engineer