The following information was provided by Danny Miller and Scott Hawley, Stowers Institute.
The sequence of the balancer in Bloomington stock was analyzed
23229 y1 w* baz4 P{w+mW.hs=FRT(whs)}9-2/FM7a, P{Dfd-GMR-nvYFP}1
and it showed that the balancer is not FM7a. It is actually FM7c from which snX2 was removed by a double crossover. It retains sequences near garnet unique to FM7c. Consequently, the entry for the FM7a-P{Dfd-GMR-nvYFP}1 balancer variant (/reports/FBba0000569.html) needs to be modified to change the variant name, the "short genotype" and the identity of the progenitor.