Nigeria #303, 560A 30k Reissued 1973-86 Definitives and 1990 Definitives, Mixed Franking on 1993 Airmail Cover to USA, Net. Est. $12

Airmail cover sent from the Government College in Ilorin on June 9, 1993 to the
University of Detroit. Franked with a single 20N, plus a pair of the 30k from the 1973-1986 issue. Together this pays 20N 60k of postage. This is an odd rate, and the best explanation that I have for this is that this cover was sent at the beginning of the hyper-inflationary period. It would seem that the airmail rate to the US in 1992 was still 60K, and hence the pair. Then in 1993, it went up to 20N, and the 20N stamp was affixed at the post office, when the sender realized that the rate had increased. The stamps are tied by light, but clear strikes of a skeleton cancel for the Government College in Ilorin (likely 2 GBP on cover, as most all other markings of Ilorin list for this amount on cover)
The cancellations list in Proud for 2 GBP and the cover value to a common destination is approximately $10 applying Gibbons’ prescribed multiplier of 2 to the Scott value of $5 for the stamps off cover. Oman is an extremely scarce destination. So, the value of this cover, taking the destination, rate, franking and cancellations into account is $12.