I read a statement that a chiton was a “fake” chiton because the sleeves had been sewn rather than pinned. The common interpretation of an “Ionian chiton” does seem to be that the tops of the large rectangles have been joined intermittently by “buttons” (though these are never actually acting LIKE buttons, but are rather sewn in place ornamentally) or pins, and there do seem to be examples for these, but there also appear to be examples where the sleeve is fully joined. Statuary provide the best examples; the artists frequently went to great lengths to demonstrate the flow and folds of garments, so it seems safe to presume that if they wanted to depict a sleeve attached intermittently rather than a seam, they would have. A few examples are presented.
In the Charioteer of Delphi bronze , it seems likely that these sleeves have been gathered or possibly even pleated.
In the next two Cypriot limestone statues, the straight line down the top of the sleeve appears to connect both sides with no indication of gapping or of hanging open.
So, it seems safe to sew those sleeves. We recreated the look of the charioteer with this linen chiton.
 The Charioteer of Delphi. Internet: https://commons.wikimedia.org/wiki/Category:Charioteer_of_Delphi#/media/File:Ac.charioteer.jpg [March 6, 2017].
 Limestone statue of a young man. Internet: http://www.metmuseum.org/toah/works-of-art/74.51.2465/ [March 6, 2017].
 Limestone statue of a youth holding a pyxis. Internet: http://www.metmuseum.org/art/collection/search/242323 [March 6, 2017].