Oubliette, LOL!!!! (I know, I know... I just can't help myself... I have to "prove to myself" these things.)
Bobcat... my understanding is that where WTS inserts [continue to] (NWT simply says "will be") could be correct. In other research I've done, the Greek word used (Strong's 1510) has several meanings, thus is a bit of a challenge to translate. One of the meanings carries an idea of 'is and will be'. Actually, here's a snippet from the Strong's definition (http://biblesuite.com/greek/1510.htm):
b. so as to indicate continuance in any act or state (Buttmann, 310f (266)): ?ν διδ?σκων was accustomed to teach, Mark 1:22; Luke 4:31; Luke 19:47; ?ν (T Tr text WH ?λθεν) κηρ?σσων, Mark 1:39; Luke 4:44; ?σαν νηστε?οντες held their fast, Mark 2:18; ?σαν συλλαλο?ντες were talking, Mark 9:4;?ν συγκ?πτουσα, Luke 13:11; ?ν θ?λων, Luke 23:8; ?ν προσδεχ?μενος, Mark 15:43 (Luke 23:51 προσεδ?χετο); once in Paul, Galatians 1:23 ?σαν ?κο?οντες, with the future (cf. Buttmann, 311 (267)): ?σται δεδεμ?νον, ?σται λελυμ?νον, equivalent to shall remain bound, shall remain loosed, Matthew 16:19; ?σται πατουμ?νη shall continue to be trodden down, Luke 21:24, and other examples c. to signify that one is in the act of doing something: ?ν ?ρχ?μενον was in the act of coming, John 1:9 (cf. Meyer edition Weiss at the passage); ?ν ?ποστρ?φων, Acts 8:28.
So, in this case, I don't fault the Society for inserting [continue to] there. It gives the idea that at the time Jesus said this, Jerusalem was already being trodden down by the nations, which was true since at that time, the Romans were the governing authority, and Jerusalem had no king.
However, for it to be fulfilled BEFORE the last days started (or at least at the very start of the last days) does not make sense in the context.