If you indeed have an "old Stash" of Portriga, i.e. before 1988 then you have been treated to some of the finest enlarging paper ever made. The micro-contrast in the shadow areas is second to none!
In 1988 Agfa was forced to make a "minor change" to the emulsion, they removed the Cadmium due to its manufacturing impact on the environment. There is a long story that goes with this and subsequent warm tone papers not worth going into here.
Yes, my small stash of Portriga is from about 1979 or earlier. I would be very interested in the "story" about this.