For me, I can see the point that all of the 144,000 have not yet been sealed, otherwise the end would have come by now, but that does not mean that there were never many faithful Christians between the Apostles and the Bible Students, as the org has claimed in the past. They confuse the number of believers with the number of ones bought from the earth to rule in heaven. The two numbers are clearly not the same and never have been.
The GB, while claiming to leave "matters to Jehovah", are still presumptuous about who they believe goes to heaven. They assume, firstly, that all their 'anointed' definitely will, but are much more coy about the possibility that any others from history will, or have done. For example, they often extol individuals from history who were 'martyrs' for Bible truths, like Wycliffe or Tyndale, etc, yet they are very hesitant to say those ones may have a heavenly resting place, yet they are adamant that their own organisation's leaders definitely do!
But scripturally speaking, that gift is not for men to decide, but only the Father.
To me, it's perfectly possible for there to have been hundreds of thousands of faithful Christians through history (by that I mean, honest-hearted though not worshipping correctly), yet only some of those selected by God to form part of the 144,000, because he's not just looking for being "faithful", but for more than that. And besides, it's His decision, not ours. Only he can read the entirety of a person's character, faith and so on, and he knows the best individuals to take to heaven to rule.
It may well be, for example, that the list of characteristics given of those ones in Revelation are literal - that they are virgins (never having had a mate means they were fully attentive on God all the time, without distraction - like Jesus) and they were executed or martyred for their faith (to surrender your life for your love of Christ would be the ultimate sacrifice, just as Jesus himself gave for us), possibly even that they are all male and are ultimately descendants of the 12 tribes of Israel (not that they would all be Jewish, but their lineage would eventually trace back that far).
After all, Revelation makes it clear these ones who become heavenly kings have these characteristics, and all attempts to explain symbolic versions of those qualities often appear forced, whereas to literally fill those characteristics would be completely in keeping with scriptural history, rather as Jesus fitted the foretold Messiah both symbolically and in terms of behaviour and heredity.
Individuals are invited to heaven not just for being 'faithful', so it's impossible to claim there were never more than a handful of 'acceptable' Christians before 1914. No human has the right to assert that - that's entirely in God's hands to determine. One of the reasons for the resurrection and Thousand Year reign is to enable previously "honest-hearted" ones to be restored to life and grow to full knowledge and perfection, so how can the org know that there may not be thousands - maybe even millions - from history who identified as Christians who God will allow to live again in Paradise because their faith was genuine, even if it wasn't all "according to accurate knowledge"? (And even today, how do we know whose faith is entirely "according to accurate knowledge"?)