Dear Billy H.,
Some PlM explanations are necessary. The standard was never 18, It began as 8 and was raised to 16 (allegedly, the records cannot confirm it totally without doubt) for a short while (only MvR can be positively identified as falling under the "rule of 16") and from Feb/March 1917 the standard reached its final form: 20 victories. It certainly wasn't late in the war, where the air war was concerned.
The rule started out as 8, or actually, Boelcke and Immelmann set the standard there. After they had won the EK I and II, the Hohenzöllern KC was up next. They got it for 6. At that time victories were still rare so 6 was pretty much the frontier. But 7 and 8 followed and the Kaiser had nothing else left than the PlM to bestow. The Crown Order was not bestowed to junior officers on active flying (with the highly exceptional case of
Rudolf Windisch). But the Kaiser certainly wasn't sorry to hand out those gongs!
The criteria for the medal were:
-a succesful defense of a fortress
-a succesful capture of a fortress
-a decisive win on the battlefield with the enemy clearly withdrawn
The first PlM went to Otto von der Linde who -with a mere squad of men- bluffed a Belgian fortress into surrender in 1914. Though not by combat, the criteria applied to him and he got his medal.
For airmen a standard had to be set, but that was not an actual matter during 1914/15. It became a matter when Boelcke and Immelmann made (inter)national heroes of themselves by downing one plane after the other. Sooner or later, they would have earned all other Prussian medals and the PlM was the next logical step after the Hohenzöllern KC.
Only the 1916 batch were for 8 victories, these men were:
Oswald Boelcke 8/40 KIA 28-10-16
Max Immelmann 8/15 KIA 18-6-16
Hans-Joachim Buddecke 8/13 KIA 10-3-18
Kurt Wintgens 8/19 KIA 25-9-16
Max Mulzer 8/10 KIFA 26-9-16
Otto Parschau 8/8 DOW 21-7-16
Walter Höhndorf ?/12 KIFA 1917
Ernst Freiherr von Althaus 8/9 (possibly 10) removed from flying status due to eye failure around June 1917 by MvR
Wilhelm Frankl 8(?)/19 or 20 KIA 8-4-17
Rudolf Berthold 8/44 murdered in Mar 1920
Gustav Leffers 8/9 KIA
Albert Dossenbach 9/15 KIA 15(?)-6-17
Hans Berr 10/10 KIA mid-1917
The next PlM aviation recipient was MvR with a score of 16. Then came Voss and Bernert, but it isn't totally clear exactly when they were recommended, for 16 or for 20? Since their scoring was so rapid, the line between their 16th and 20th victories is very thin. In fact, Bernert scored #17-21 in one day...
While politics certainly played a part in German medal awarding, it was mostly when states were called upon to invest sons of other states with their awards. Prussia-Bavaria and their continuous bickering are excellent examples, as is the case of the then NCO Rudolf Widisch who received the Crown Order from the Kaiser when the Oberste Kriegsherr's attempts at promoting Windisch to officer status had been foiled by the Saxon authorities (who had the right to promote/demote its own soldiers).
It is my impression though that very few aviation awards are of the political type. Doesint matter if teh standard is 8 or 20, the standard was set and had to be met - that's final! Only two cases where the 20 mark wasn't reached: Goering (I hear the crowd already!

) and Kissenberth (a Bavarian of all people!). Goering unexplicably got his medla for "only" 18 victories while Kissenberth was so severely wounded after his 19th victory that he'd never return to combat. He was given the PlM anyway, a nice gesture I would think.
The room is open to receive differing opinions...
Kind regards,
Reinout