UNESCO/Nubian Monuments - Abu Simbel (no longer) Mystery Stamp!!

These were sold to me as "Unrecorded Revenue Stamps", issued in 1982. Originally with a value of 10 Dollars, they are overprinted "2 Dollars". I only bought them because they depict the Temple of Abu Simbel but I cannot find any information about them anywhere...

So if you know anything about these stamps, do post a comment :¬)

April 2012 update - I now have it on good authority that these are consular stamps used when granting visas.

April 2019 update - thanks to Jerry who pointed me in the direction of the Egypt Study Circle and the information below (Source: http://www.egyptstudycircle.org.uk/QCs/QC261.pdf).  

In March 1960, just two months after work on the Aswan High Dam was started, the Director-General of Unesco, the United Nations Educational, Cultural and Scientific Organisation, launched a worldwide appeal to save the 3,000-year-old monuments of Nubia from being flooded up to 50 metres deep by the dammed waters of the Nile.  Over the next 20 years money and aid of all sorts were gratefully received in a defining example of international solidarity, and dozens of temples and monuments, including the two temples of Abu Simbel and the temple complex on the island of Philae, were rescued for posterity. 

As part of its economic contribution, the Egyptian Government required all of its visitors to pay a nominal $2 fee, in the shape of a consular revenue stamp to be placed in each and every arriving passport: remarkably, the only Egyptian stamp with face value in a foreign currency. Peter Feltus, in his Catalogue of Egyptian Revenue Stamps (1982) listed three issues, but more recent discoveries have added greatly to our knowledge. Here is a full listing as far as is known:

Fig. 1, 1962 (Feltus p.51), or perhaps 1964, dull purple and pale green, inscribed UAR and equivalent at top left, watermarked UAR, face value $2. 

Fig. 2, 1971 (Feltus p.53), as last, but inscribed ARE and equivalent at top left instead of UAR. 

Fig. 3. 1981 (Feltus p.54), colour changed to greenish blue and dull orange, design redrawn but essentially same, perforation changed from 13 ½ x 13 to 11, watermark large eagles sideways. 

Fig. 4, 1983 (so unrecorded by Feltus), as last, but with inscriptions redrawn, most obviously in shape and curvature of the figure 2 in both European and Arabic languages. 

Fig. 5, 1985, colour changed to blue-green and yellow, and face value increased from $2 to $10. But this may have been a step too far – was it visitor pressure or a government realisation that a mistake had been made that led to the $10 value indicator being surcharged with bars and lettering indicating a return to the original $2 value? This stamp has not yet been recorded on passport pages or other documents. Was the unsurcharged stamp ever used? 

Fig. 6, 1988-89, colour changed to brown and buff, but like the last, with original face value of $20 surcharged back to original $2. This issue has been seen on a 1988 passport page.