He 59 Wnr 1991 NE+TD

[Seaplanes]

Locally formed or temporary formed is my translation of the Luftwaffe term "Auf dem Kommandowege aufgestellt". Such formations were done from time to time and normally for a period of maximum six months. If such a unit lastet longer, it was normally "Etatisiert", which means that the unit is made permanent and was granted extra supplies and personnel.
However, for the 1./706 the situation was that the unit had too many aircraft on strength so some aircraft had the unit code 6I+ - H and some 6I+ - K. This was the same as for 1./196 which also had so many aircraft on strength that some were marked T3+ - H and some T3+ - K, although a 2/196 did not excist until late in the war.
The 2./706 did excist for a couple of months only. May be Jörn Junker ca constribute with more info on this. 1./706 gave up about 50 % if their He 59's in mid June 1940, so I would anticipate W.Nr. 1919 to be transferred about then. The aircraft probably first went to Walter Bachmann in Ribnitz to get the most basic ASR equipment installed before being delivered to Seenotflugkdo. 3. I have no excact date.