1975 was a major set-back for Jehovah's Witnesses, but it was a one-off event. The numbers went in decrease for three years or so, but then they began to pick up again. The advent of the Internet is probably different.
We could say that the Internet has been having an effect since the late 1990s when many first went online, and this has been reflected in the much slower growth in the Yearbook statistics from that time. But people are still becoming web literate all the time, especially now more so older ones. Yet other Witnesses who have been on the web for years may not have ever looked for apostate sites. At some point it is likely that many such ones will have a look for various reasons, with varying outcomes.
But the point is that the new dynamic to the control that the Watchtower religion maintains is continually effected by the Internet year after year. It is not something that they can ignore for five years, say sorry on the fifth year, and spend the next few decades ignoring it until it is forgotten.