"Sienese Master, 15th century": circle of il Sassetta?

Nagel, from Germany, sells on 28 February 2019  as lot 701 an "Italian" Madonna estimated at 1,500 Euro.

The description indicates that the back of the painting has an inscription identifying it as a 15th century Sienese Master, showing a Madonna from an Annunciation, and that it was owned by "J. A. Ramboux" who they identify with Johann Anton Ramboux (1790-1866), a major early collector of Sienese art.

The painting to me looks convincing, so it may be an original as described on the back. In that case, it should be worth a lot more, perhaps closer to 10,000 Euro, as a good, attractive example of the common paintings in Siena and surroundings for about 100 years.

The closest artist I have found so far is Stefano di Giovanni, named Il Sassetta, who lived from ca. 1390 to ca. 1450 in Siena. His Madonnas have similar folds in the clothing, similar poses (though the hand position here is unique, even if the hands are the worst part of the painting), similar headdress... The way the face is painted also is quite similar.

There are, always assuming it is an original and not a 19th century fake, probably even better matches to be found by people specialized in this period and region, but it may give an idea about where to look!

UPDATE: sold for 55,000 Euro! Way more than even I expected.