Help With Value Of Swiss Sonderfulg Airmail Cover C19 & C26

This 'Sonderflug' Special Flight cover from 1938 has a very fine pair of Scott C19 cataloging $32.50 each in the 2010 catalog as well as Scott C26 at $6.50 which it says was not sold to the public but affixed by postal officials so no price for mint is given.

Does Michel offer values for these stamps on cover?

(I don't collect covers but am pretty tempted to soak these off the envelope and place them in a couple of albums.)

I would not remove them from the cover as a Stamp by itself might be worth a dollar, leave it on cover and it's worth 5 dollars. The attraction of the cover is the complete cancels, the destination, and basically the whole travel itinerary...Not to mention it's a registered cover. So basically the Stamps will almost always be worth more on an intact cover.

First stamp issued 22.05.1938. Indeed, originally sold only affixed on cover, later only used (bw. 23.05-31.05.) Still(according Michel) there are a very few unused mint ones, Michel values them at 14000 Eur (!!) in 2005. Used value in 2005 is 7 eur for used, and 10 eur for FDC. And I guess this is an FDC, at least considering the date of issue. I only have an older `Zummstein` (swiss) catalogue - 1963, for the first stamp it offers a bit higher value on cover (used-5 Fr, on cover 7 Fr.) Guess this still stands, so there is a premium for them on cover.