RE: question with kit building
Jig tabs are sometimes added to symmetrical ribs to keep the aft end of the ribs up so that the centerline of the ribs will be level with the building board. They are little extensions near the trailing edge of the rib which are cut off when the wing panel is removed from the board. Is it possible that you removed them when taking the ribs off of the sheets they are cut from?
If the tabs are missing it is no big deal. The tabs are handy when the manufacturere cuts our the ribs with a metal die or a laser. But they are not practical when scratch-building and cutting the ribs out by hand. In those cases I just put a balsa stick of appropriate size to shim up the ends of the ribs. Simple and does the job.