Change in filenames?

I’ve been using a set of files downloaded for LAI Data, from 2014 -2020.
there are 6 groups, LAI, LENGTH-BEFORE, LENGTH-AFTER, NOBS, QFLAG and RMSE, all with the same format:- c_gls_LAI300-XXXXX_202002100000_C_PROBAV_V1.0.1.tiff
all until the timestamp 202003310000.
then the filename changes to:- c_gls_LAI300-RTZ-XXXXX_202005200000_C_PROBAV_V1.0.1.tiff
where Z is either 0,1 or 2.
I cant find any reference to this in the documentation, please could someone explain it?