The old pre-1995 teaching had a definite start-date for the generation, i.e. 1914 (or those at a certain age in 1914). It was the end-date that was indefinite but bound by the usual limits of a generation. Then in 1995, the generation was redefined as "the peoples of earth who see the sign of Christ’s presence but fail to mend their ways". The "sign of Christ's presence" was still believed to have started in 1914, but the new interpretation allowed the generation to continue indefinitely, as the whole period between 1914 and Armageddon was held to manifest the evidence of the "sign of Christ's presence". The Society denied that "Armageddon is further away than we had thought", but in fact that is how things ended up by the course of events, as the older teaching once construed the end coming no later than the 1970s, or no later than the end of the 20th century. The new interpretation only defined the generation as those alive during Christ's presence and at Armageddon. Although the endpoint was unknown, the generation was defined more by its endpoint than its startpoint (other than the fact that the generation dates after 1914, which is true for almost everyone alive today).
Then in 2008 the Society redefined the generation again, claiming that it is composed of those "anointed ones [who] make up the modern-day 'generation' of contemporaries that will not pass away 'until all these things occur' ". The inclusion of the word "modern-day" would seem to prevent one from regarding the "generation" in a non-literal sense as all the anointed throughout history. These are all contemporaries "living at a particular time", like any other generation. The Society probably still maintains that the generation is set within the period of Christ's presence after 1914, but there is no startdate at all -- as indicated by the fact that the article makes a special point that the generation of Joseph included those born before him and those born after him. This vagueness would allow the understanding of the generation to keep up with the times as 1914 recedes further and further into the past. The generation seems to defined rather by the endpoint, such that the promise about "this generation" not passing away "suggests that some who are Christ's anointed brothers will still be alive on earth when the foretold great tribulation begins". Although the Society claims that the generation of anointed contemporaries is presently in existence on the earth (on account of Armageddon being sooooo close), they could technically claim the same 100 years from now with respect to the "anointed" still alive in that day. Rather, it is when the great tribulation begins (and then subsequently Armgeddon) that the generation would clearly be defined as the one that witnesses both the "sign of Christ's presence" that has been in effect since 1914 and the final events of this system of things.
My 2 cents, as usual. :)