They have always claimed that they are going back to the "true Christianity" as practised in the 1st century, so they agree those early followers were true Christians. This of course ignores the proof that there were a good number of Jesus Cults in the Ist century, with wildly differing beliefs.
But quite obviously the number of Jesus followers must have been great enough before the end of the Ist Century, when the Borg says " Apostasy" began, to have more than filled 144,000 places in heaven.
Just another stupid JW Doctrine that does not stand up to scrutiny.