Karges includes in his manuscript (AM B 340, owned by the Staatbibliothek Berlin) at least three works composed by Heinrich Scheidemann. One of those three appears without Scheidemann's initials in this manuscript, but is known to be a composition of Scheidemann from others manuscripts. It is not unlikely that ons or more of the other anonymously transmitted compositions in manuscript Am/B/ 340 is by Scheidemann's hand as well, though it is impossible to know for certain.
In his book, "Heinrich Scheidemann's Keyboard Music: Transmission, Style and Chronology", Pieter Dirksen writes writes about Am.B 340: "Scheidemann is represented here by three 'fantasias', two of them with his initials (wv 83 and 43a), one anonymous (WV 74). Their text along with their titles [...] is thouroughly unreliable, as a comparison with the tesxs of Toccata wv 43a and the Cantzoenn wv 74 in KN 209 demonstrates. On the other hand, there is no reason to doubt the authenticity of the Fantasia (?) in d wv 83, only the version in which it is given here."
From the works I transcribed untill now from this manuscript it is clear that Karges adapted the originals to his need, making them shorter or in a few cases longer, or mixing them with other musical material, sometimes certainly and sometimes possibly from his own hand. As fas as I know this 'fantasia' by Scheidemann appears in no other manuscript, and this version of Karges is the only source there is. How much of this composition is truely by Scheidemann and how much of the original was perhaps cut away is a question that will probably never be answered. If it wasn't for Karges, we would not even have this version.
The piece starts with a fugato introduction. The chromatic theme appears ten times in the introduction and an eleventh time in dimunition. The theme of the fugato kicks of the Echo Fantasia that follows it. To my ears the music of that part flows naturally and elegantly. If Karges made cuts in a original that was longer than this version, they are not noticable in the result. The only point where you might suspect a cut by Karges is the conclusion of the composition. It ends rather abruptly, though that still might be how the original was brought to a conclusion.
How much of this piece is by Scheidemann and how is of Karges' invention in unknown. You might view it as a shame that Karges did not just copy the original note for note. You might also view it a lucky circumstance that Karges used it for his needs, and that there still is this very playable and enjoyable version of an unknown original. Wihout doubt, my view is the latter one.
The recording was done with the Hauptwerk software and the sampleset the Transept organ in the Laurenskerk, Rotterdam, made by Sonus Paradisi.
Score available here: http://partitura.org/index.php/heinrich-scheidemann-wilhelm-karges-fantasia-in-d-wv-83