Lot 5 United States #112, 114 1c Buff and 3c Ultramarine 1869 Pictorial Issue, Combination Usage on 1870 Inter-Treaty Mail Cover From US to France, Via London, Est. $500-$750

Lot 5 United States #112, 114 1c Buff and 3c Ultramarine 1869 Pictorial Issue, Combination Usage on 1870 Inter-Treaty Mail Cover From US to France, Via London, Est. $500-$750
A very fine cover, sent from an indistinct location in the US to Paris, in April 1870. Franked with a strip of three 3c ultramarine and a single 1c buff, overpaying double the 4c British Open Mail rate to the UK. Red London transit backstamp and black straight-line “shortpaid” struck by Munro & Co to indicate that the postage was only paid as far as the UK. An oval GB 10c accountancy mark has been struck on the front as well as a French transit stamp which reads “Amb.. April 14, 1870”.There is also a 5 decime postage due marking on the face. It looks like a squiggly line, but from my examination of several covers from this issue sold by Robert A Siegel in their Coulter sale of the 1869 issues (May 12, 2006) it is clear that this is a postage due marking. (https://stampauctionnetwork.com/y/y91134.cfm). Paris arrival backstamp with an unclear April 1870 date.
As far as value goes, the covers to France that had 10c stamps paying the rate all sold for between $325 and $1,100. Those franked with other combinations of stamps for the 4c and 8c rates sold for $600-$800. So, this cover should have a value of between $500-$750.