US: Airmail labels

Here are some very rare airmail labels from USA.

Year: 1928, Ungmmed. Günter Mair's catalogue no: - USA-C-12a, perforated 12 ½ , sheets of 25 labels 12a + 5 labels 12b, plane in red, red/blue/white, 6******

Year: 1928, Ungummed, Günter Mair's catalogue no: - USA-C-12b, perforated 12 ½ , sheets of 25 labels 12a + 5 labels 12b, colours inverted, plane in blue, blue/red/white, 6******

Year: 1928, Gummed. Günter Mair's catalogue no: - USA-C-19, imperforated, black-blue/white, 
5*****

Year: approx.1935, Gummed. Günter Mair's catalogue no: - USA-C-41, imperforated, size: 101x53mm, blue/red/white, 5*****