Antwerp local in 1919 with insuficient postage

This cover was sent on 22 April 1919 locally from Antwerp to the Antwerp Central train station with only 8c of postage. The insufficient franking caused it to be affixed with 2F60c worth of postage due. The 2F definitive stamp of 1915 (Scott No. 120) overprinted with a big T is a rarity, especially on cover.

Characteristics: 2c+2c in block of six with a block of four of the 15c definitive of 1915 and the 2F definitive of 1915, all five overprinted with T Total franking = 6c, Postage due = 2F60c Anonymous sender No cancel of arrival Some wrinkle
Estimated value: $120 [Auctioned by Olivier Simons in October 2007]