Postage stamps should never have their cent values printed on them. Such stamps should indicate what class such a stamp is valid for, such as First Class, Postcard, etc. Rather, all such stamps should be worth whatever the current rate of that stamp class is at the time of usage, regardless of when that stamp was printed. The same can be done for all other classes of stamps, as well.
If for whatever reason such postage stamps cannot be of the “Forever” type, but do have fixed values, then such values should be printed on them. This should apply even to the interim stamps that are circulated during the transition period before the new stamps arrive. There is no acceptable reason for not having these values printed on all such stamps.