Like Contrapunctus 14, Fugue 4 of Das Wohltemperierte Klavier (BWV 849) is a fugue with 3 themes. Looking at the length of the piece as well as the length of the themes, Fugue 4 is much shorter. Nevertheless a comparison can be made.
Three themes of Fuga 4 (bwv 849)
Three themes of Contrapunctus 14 (bwv 1080-19)
The three themes of fugue 4 and Contrapunctus 14 have comparable characteristics.
Above the graphics of Fugue 4 and Contrapunctus 14. The beginning of the fugue is common, the introduction of theme 1 in all voices is similar to Contrapunctus 14. At bar 44 theme 2 is introduced, theme 3 is introduced at bar 49.
The overall structure of theme 2 at the quindecime (2x octave) in Fugue 4 is the same as the overall structure of the inverse of theme 1 at duodecime in Contrapunctus 14. Also the appearance of the themes at the second highest level is comparable. An end of Contrapunctus 14 comparable with Fugue 4 would be a development to the dominant and to the tonica with a pedal point.
Also a comparison can be made between Contrapunctus 14 and Contrapunctus 2 of Die Kunst der Fuge. Among other things these pieces have comparable dimensions of the first theme and a comparable exposition. See the graphics below.