I'm sorry to keep harping on this, but IMHO, it is huge...
Jehovah's Witnesses teach that there are two and only two Christian hopes:
A: The heavenly calling
B: Surviving the great tribulation (i.e. The earthly hope)
This has been discussed every single year at every single Memorial for as long as I can remember.
Jehovah's Witnesses therefore teach that the heavenly calling was the only hope from Pentecost clear up until the proximity of the great tribulation made the identification of the second hope possible.
That happened in 1935. The clock started ticking then and there and this is openly acknowledged in their literature:
"God’s infallible Word depicts this group as ‘coming out of the great tribulation,’ being survivors of it, living right on into God’s New Order without ever having to die. (Revelation 7:9, 10, 14; John 11:26) The early members of this group are now in their 60’s or 70’s or older. Jehovah did not allow the ingathering of this group to begin too soon. The “great crowd,” including many of the earliest members thereof, will survive into the “new earth.” (Survival Into a New Earth p. 185 emphasis mine)
https://www.jw.org/en/library/books/Survival-Into-a-New-Earth/The-Countdown-Nears-Its-Zero-Hour/
This quote is nearly 40 years old now and the passage of that time has made it glaringly obvious that it is completely wrong. 1935 was 86 years ago and even a 15-year-old at the time would be over 100 today.
Jehovah's Witnesses sometimes get details wrong that are not essential to their faith (Like what an equinox is for example) but this does not fall into that category.
The Christian hope is an essential matter of faith. It's what JWs believe that Jesus died for and it's what they teach at their Memorial.
And they were (And still are) wrong