October 9, 1238, James I of Aragon retakes the Spanish city of Valencia from the Muslim Moors
October 9, 1239 is when the central mosque of Valencia was converted into a church
If they're actually planning something for Sunday Oct 9 in NYC, they wouldn't be going after the subways. The symbology of the date would point them at St Patrick's Cathedral during services, or some other church or group of churches
St. Patrick's Cathedral will be heavily guarded by armed men all weekend. You wouldn't know it, though, by looking at them. Cops in mufti.
If that happened, we'd find an interesting ally in the Vatican.
10+9=19