Which do you not understand in both statements the word "begun" or "starts"? We can help you from there. :) When you reply have a dictionary in hand and a pencil with an eraser and paper, maybe several sheets. You can always rewrite what you make a mistake on.
First of all, there was only one unified congregation [some refer to as a church] not many. The word congregation can mean all congregations as a whole or individual local congregations of that whole. They all taught the same things. By the middle of the first century apostasy had already started and by the end of the century sectarianism had developed. (2Thessalonians 2:3, 7 9; Revelation 2:2, 6, 14, 15, 20) Though, some Christians remain faithful to the teachings of Christ, as Jesus gave them commendation on their good while he gave them admontion and strong counsel on what they needed to improve upon or change. (Relation 2:2, 3, 6, 9, 10, 13, 19, 24, 25)
All from the first century until undoubtedly 1919 C.E. were chosen to be of the 144,000. Since 1919 C.E. those with an earthly hope have been gathered along with the remaining remnant of the chosen. In 1935 C.E. the great crowd with the earthly hope was officially identified. God continues onward to complete the number of the 144,000 while gathering a great crowd which no man can number for surviving the great tribulation.
All other denominations of churches that veered away from the original teachings of Christ came from the initial apostasy and teachings of sectarians. From these, by the 4th century, the teaching of the trinity developed. These churches also came to teach other pagan doctrine such as the immortality of the soul, hellfire, eternal torment, and many other non-scriptural teachings that have been passed down by tradition. These apostate churches are responsible for many deaths in the name of religion, such as the crusades and the inquisition, to name two instances. The true Chrisitan congregation remained neutral and faithful to Christ during these trialsome years of their particular generation and time. While this went on God was still choosing members with the prospect of becoming of the 144,000 down until our day, as wheat amongst weeds.
EDIT: @ isnrblogdotcalm; I already know that some of the 144,000 will survive armageddon. The Bible reveals this. We never said none would. We do not converse with those who unrepentently and defiantly oppose the true God, the spirit of truth, the word of truth [the Bible], and the true Christian congregation of Jehovah's Witnesses. By what you admittedly stated, I am done reading your responses and responding to you or about what you might and will have said.
EDIT: If you too "I Try" are also disfellowshiped or an apostate [which you seemingly are] we are also done.