Thank you very much for these files.
Baron Jules Goossens-Bara's insignia has nothing to do with Poland, even less with the province of Flemish Brabant, the arms of which were invented... in 1995 !
In Above Flander's Fields, there is a biography of this pilot, where it is said that :
"During this period (June 1917) Goossens had a personal marking which was practically the same as the Polish national marking : a two-coloured square divided in 4 squares, although the colours are not known."
There is, however, no reason to believe they were red (but they might have been).
At that time, Goossens was part of the 1ste Escadrille (on Nieuport), NOT the 9th. The 1st escadrille only became the 9th after the reorganisation of March 1918, flying Hanriot then. By that time, Goossens had left the unit to join the 7th Escadrille.
The 1st Escadrille's insignia was the famous thistle.
The insignia doesn't look either like the one of the 11th escadrille, shown above, the so-called "cocotte" (paper hen), which isn't in a square.
Goossens was made an Adjudant on 17 June 1917 and a Sous-Lieutenant in November of that same year. He ended the war with 2 victories (one of these shared), but he probably had 2 more, that he didn't even claim.