Beginning in 1905, Germany began phasing in the use of watermarked paper on its new issues.
This practice eventually led to the introduction of new Yacht issues which were similar to the 1900/1901 issues, but featured a lozenge-shaped watermark.
The 1915/1919 Yacht Issues were never postally used due to the fall of the German Samoa. The stamps were only sold at philatelic sales windows in Berlin.
MiNr. 23 I A is a “peace printing” issued in Jan 1915, and therefore shows different qualities from the remaining “war printing” (Apr-May 1919) issues of this set. It is lighter in color overall, with better quality paper and printing.
Additionally, in 1923, the Reichspostministerium (German Postal Ministry) conducted a sale of old German postage to help fund German reparations payments to the Allies. Compete sets were sold in envelopes specifically printed for this purpose.