#4 is not an official designation. It only signifies the order in which these projects have been presented in the source from page 146 to 147.
A total of 6 different designs are shown.
Source : Die Deutsche Luftrüstung, 1933-1945 (Band 1) - Heinz J Nowarra
P.146
Scan of the drawing : https://preview.ibb.co/mnxiPK/lfajet4.jpg