Technically, an overprint is the additional layer of text or graphics added to a banknote after it has been printed. Official overprints are those which are recognized and formally released by the Banko Sentral ng Pilipinas (BSP) to celebrate a particular event. Private overprints on the other hand, are those made by private groups on demonetized or retired banknotes. Private overprints are also referred to as Unofficial overprints. Over the years, it’s been a subject of debate, still most numismatist and collectors do consider these notes as a collectible.
Below is a 2 part video as featured in ABS-CBN’s “Kontrobersyal” hosted by Boy Abunda. The video talks about the controversies raised on overprints, which gave out very interesting points on each side.