The 100pf is not an inflation issue but the first issue in rentenmark after the hyperinflation period. The rest of the series was invalidated 31 January 1928, but the 100pf was good until 30 June 1934, according to Michel.
It is a common misunderstanding to think that the red circular cachet proves a cover was flown by Zeppelin. This is a good example of a cover that was not. In my estimation there are more of this kind that were not Zeppelin flown than there are of ones that were. If you look closely at the red circular cachet you will see that it has both a Zeppelin and a seaplane in it. The reason is there were two kinds of German airmail service to South America in the 1930s. One was flown the the German airline DELAG which operated the Zeppelins. The second was more frequent and was flown by the German airline Lufthansa which operated with a combination of land planes and seaplanes. This red circular generic airmail cachet was used on all German air mail - both that which was flown by DELAG on Zeppelins and that which was flown by Lufthansa on their land plane/seaplane service and this generic red circular cachet with a Zeppelin and a seaplane was designed to be used by both kinds of service. The only way to tell if a cover is Zeppelin flown is not by the circular red cachet, but rather by the comparing the postmark and back stamp dates will need to match exactly with the dates for Zeppelin flights listed in the Zeppelin mail catalog. Everything else with this red circular cachet was flown by the Lufthansa land planes/seaplanes.