Austria as a political entity got that name about 1000 years ago. The first recorded use of the name was Ostarrîchi (ostar/Eastern rîcchi/Realm) in 996AD, when it was just a Margravate of a larger Duchy & a minor part of the Holy Roman Empire (not an independent nation per se)... but that's enough "Austria" that a sneaky author (like Jim) might IMO stretch the time out that far, if he wanted. It's a long f'ing timeperiod to look for died-young composers; tho Mozart (died at 35) certainly looms large in any such list; and Schubert died even younger!
Not sure what the point is here with all due respect. Mab still could have been Queen for a thousand years, still look young and pretty as a now mostly Fae. Who knows what child baring age is for a Fae? So Mozart or Schubert still could have sired her twins.