SE5

Does anyone know what that line is, visible in many photos somewhat ahead of the aileron, underside upper wing???
Im looking thru some of my ref. works (Squadron Signal, etc) Some views seem to show it under lower as well, but definitely not visible in image 3rd protoype page 6 (SE5a In Action). What am I seeing in image of Ball's a/c page 12?

Also, I have Charles Bregret's(sp??)booklet with scale drawings, My take is these are relatively accurate for fuselage, but fall short in wing detail. Any comments about these. Also anyone comment about Replicraft's accuracy?
finally, Has anyone done decent drawings of the earlier SE5 (no a!)??
Thanks
Charlie