I know the rules for aromaticity. But this case is difficult for me.
Regarding the smaller ring, I guess the sulfur contributes one lone pair of its valence electrons into the system. This means from the nitrogen (in the 5-ring) only one electron is needed for the π-system (with 6 electrons). But this nitrogen atom has only one lone electron pair, thus one of the electrons would not be part of the π-system of the smaller ring. However, this nitrogen atom in the 5 membered ring is also part of the 6-ring and there it could share both of its free electrons to this larger ring. Then the second nitrogen which is only in the 6-membered ring could contribute one electron only to the aromatic system, and thus having a happy free lone pair left.
What do you think of that? Which rules, logic or reasoning can confirm this? And isn't it a problem that the first nitrogen shares one electron with the 5-ring and the two with the 6-ring?
Also, is there software which can predict this reliably? I haven't found anything so far.