I had to play a waiting game for this nice sheet of Biafra, SG4 half-penny overprinted Nigerian stamps.
They debuted on eBay for a certain price. Too expensive. No-one bought. I waited and eventually they came back for sale at half that price. Too expensive still and no-one bought.
Finally they came back at a quarter of the original price, to my relief in case someone else nicked them when I wasn’t looking. I bought the sheet and here it is. It’s quite small at 22.5cm by 15cm.
During periods of unrest, war and different types of conflict, an administration may find itself with plenty of stamps but none of their particular political unit. Overprinting is a very common solution to this problem until they can get their own stamps designed and printed.
That’s just what happened in Biafra after it seceded from Nigeria in 1967. Later on, stamps became a source of revenue rather than used for postal purposes so today, genuinely used Biafra stamps are more valuable than mint ones.
But we have to look out for the “UMUAHIA” postmark on Biafra stamps as this was often used as a cancel to order or CTO postmark, i.e. it was not a genuinely posted letter or article.