I could use your help and expertise in deciphering the annotations on this letter, sent from Sweden to the Netherlands via Stralsund on 7 June, 1852. This was just before the new Swedish-Prussian convention became effective, so it must have been treated according to the convention of 1847, with total postage 8+8 (2x4) sgr or 24+24 skilling banco.
My theory as follows:
-the crossed-out 8 and 9 in black in the upper right corner are letter bill numbers; the first the Swedish one, and the second the Prussian one?
-fr 4 in blue on the back is a Prussian annotation for the weiterfranco to the Netherlands of 4 sgr
-the crossed-out 8 in blue in the lower left corner is the Swedish share of postage of 8 sgr, according to the 1847 convention
-this also corresponds with the 24 in black in the upper right corner, which I assume is a Swedish annotation for Swedish share of postage in skilling banco
Then the question remains about the blue annotation in the upper left corner on the front; is this a "fr10" or a "fri0"?
-fr10 would have been the correct total postage of 10 sgr after 1 July 1852, but this rate had not yet become effective.
-However, the Dutch-prussian convention with the new rates was already effective at this point. I tested the hypothesis that the Dutch-Prussian convention could have been used by Prussia to measure out the Dutch share, but then that share should have been 2 sgr and not 4, as is written on the back. The letter is with contents, and is by no means on the border of being a double weight letter
The other theory I have is that the annotation is Swedish and reads "fri0", and that the letter was treated as a free letter up to Stralsund.
Can anyone help shed some light on this and solve the "mystery"?
Many thanks in advance for your assistance!