Yemen forerunner

Historically the port of Aden was a British Colony at the entrance to the Red Sea. Britain in the 19th century ruled India , and had colonies in Ceylon , Singapore and Hong Kong, and effectively controlled the Government of Egypt . The main trading route from India to Europe through the Suez Canal meant Aden became strategically important For the large numbers of ships connecting Europe and India .

One of the major shipping companies was the British Peninsular And Orient line , P&O . Passengers who wanted comfort and the shady side of the ship through the RedSea to and from India booked cabins Port out , Starboard home...........POSH became the word used for 1st class comfort.
Mail could be exchanged from ships passing through Aden at the British Post Office about mid way between UK and the Far East. For convenience until Aden issued its own stamps Indian stamps were used.

Hi splycos ,

This is probably in the wrong thread but I'll give you an answer anyway. Yemen has had a much troubled past which, tragically, continues to this day. As far as the stamps are concerned, the situation is complicated. I'll give the story according to Stanley Gibbons, other catalogues may give a different story. 

In Stanley Gibbons Stamps of the World there are multiple entries for Yemen.

'Yemen in Southwest Arabia, ruled as a kingdom and imamate until 1962. From 1962 stamps were issued concurrently by the Republican Government and the Royalists...In 1990 the Yemen Arab Republic and Yemen People's Democratic Republic united as Yemen Republic (combined)'

In addition, many of the Republican Government and Royalist stamps are relegated to an Appendix on the basis that they were 'either issued in excess of postal needs or were not available to the public in reasonable quantities at face value'. Almost certainly this is what you are showing. They are listed by year, up to 1970, but not accorded catalogue numbers and are not illustrated.

Hope this helps,

Daniel