In 1940, due to postal rate adjustments and the introduction of parcel taxation, the highest values of the Dr. Sun Yat-sen Definitive Series printed by Dah Tung in Hong Kong were repurposed as postage due stamps. This transformation involved applying a typographic four-sided overprint in Sung script (暫作), meaning "temporary use," onto the $1 and $2 denominations. The overprinting was carried out by the Dah Tung Book Co. and resulted in Scott J67 ($1 green) and J68 ($2 brown), both now serving as high-value due stamps. These mint never hinged blocks of four represent the complete issue and exhibit deep original color, full gum, and sharp overprints. Historically, the reuse of regular postage designs in this context illustrates wartime pragmatism and administrative adaptation under the Nationalist government. The stamps are very fine with intact perforations and clean margins, an excellent example of postal fiscal policy during conflict. Estimate "$240 – 280"