While the WTS now considers the "other sheep" and the "great crowd" to be synonymous, the "great multitude" or "great company" was considered to be a secondary heavenly class who did not qualify to be kings and priests but assisted the little flock like the Levites assisted the priests.
Looking at CTR's comments it seems that the "other sheep" were those not being gathered out during his time, just the "little flock," and that the separating of the sheep and the goats would take place during the Millennial age on earth. These people would be the "other sheep."
Here are some comments on the "other sheep" in Russell's day.
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Other sheep -- There are two classes of sheep: obedient ones, easily led by the voice of the shepherd, and a more listless and somewhat wayward class who need some driving and guiding with the crook. R1648:2
Others who will become the Lord's followers under different conditions and a different call. R4784:3
These other sheep will include all of mankind who, during the Millennial Kingdom, will be glad to avail themselves of the great provision the Lord has made for them in his plan. R5694:1, 5490:6, 4940:6, 4157:5, 3528:3, 2442:1, 1919:1, 1648:2, 1374:5, 655:1; NS272:6
These other sheep are particularly mentioned by our Master in the parable of the Sheep and the Goats in Matt. 25:31-46. R4784:6, 3528:3, 2606:6, 701:2; NS181:5, 272:6
"Israel after the flesh" will not be neglected; for though of another flock, they are under the same shepherd. R633:5
While this may be particularly applicable to the sheep of the next age, it may not be amiss to apply it now to those who are received from amongst the Gentiles. R4732:6
The view that we who are of the Gentiles or "other sheep" mentioned are now being brought into the one fold is not correct. We were not the Lord's sheep at all at the time of this parable. R3528:2
Not of this fold -- Not of the Little Flock of this Gospel age. R3268:3
They will be of a different nature from the flock which the Lord is selecting during this Gospel age. R5694:1, 5491:1
He has not yet begun to bring the other sheep; he is still taking the flock he first started to call, namely, spiritual Israel. NS412:2
The entire Millennial age will be required for the finding of the Lord's true sheep amongst the world of mankind. R3528:3, 3268:3
At that time the present flock will have passed beyond the veil into the Kingdom and its full glories. R4158:5, 2673:6
The Lord intends to use the very elect Little Flock of this Gospel age to carry his mercy and favor to all, and to give them an opportunity of becoming members of the human flock. R4158:6; NS412:6
One fold -- In the Revised Version and Diaglott: "one flock." R4159:1
The two flocks will come back into harmony with God, but the one flock will be of the heavenly fold while the other flock will be of the earthly fold. NS412:6; R4732:6
Eventually all of God's creatures on various planes of being shall be recognized as one family of God. R3268:6
The flock will be one, but the sheep will be of various natures on various planes of being. R4159:4, 4940:6
But neither should we forget that God has other sheep, not of this flock; and that he has provided that the fullest degree of natural evidence shall be given to those other sheep, the faithful of whom shall have everlasting life also, though on a lower plane or nature than the little flock now being selected, who are required to walk, if at all, by faith and not by sight. R1467, page 335
GREAT MULTITUDE OR COMPANY
Who do not prove sufficiently zealous to be counted with Jesus as "more than conquerors," who, nevertheless will prove not unfaithful in their final test. R4998:1; Q604:T,1
Those loyal, but not promptly obedient, children of God, overcharged, with zeal not according to knowledge, and more or less contaminated with the spirit of the world. D578; C364
This Great Company fails to maintain its place in the elect, because of insufficient zeal for the Lord, the Truth and the brethren--because they are partly "overcharged with the cares of this life." (Luke 21:34) Nevertheless they are loyal to the Redeemer and have not denied his name or his work. F169; R5532:6
Their love and zeal are not such as impel them to perform the sacrificing they covenanted to do. They fail to put, or keep, their sacrifices on the altar. They fail to overcome. F127, 93; Q604:1 Who will have life on the spirit plane. R5138:1, 2067:4
They will have everlasting life as angels have it, but will lose the prize of immortality. A214; R281:4
Who will come to spiritual conditions, but through great tribulation. R428:4, 355:6
I know of no scriptures which teach that any but the Little Flock or Bride company, and the company who come out of the great tribulation, will ever be given spiritual bodies. R37:6
Antitypical Levites, associates and servants of the Royal Priesthood. They will receive directions from the priesthood and will be teachers of the people. R5418:6, 5066:5, 4757:5, 4579:1, 4537:4; CR80:5; SM636:2, 637:T The scapegoat class of Lev. 16, who must suffer destruction of the flesh. R4652:1, 5138:1, 4273:3, 4035:4, 3868:2
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