Christ showed Himself to the Jews during His mortal ministry.
He showed Himself to the Nephites after His resurrection.
He visited others, who have also kept records of His appearances to them. The full extent of the records that have been kept has not become apparent to us yet. Nephi would report in the final summation of his lifelong ministry the following about the many records to come forth:
"Wherefore, because that ye have a Bible ye need not suppose that it contains all my words; neither need ye suppose that I have not caused more to be written. For I command all men, both in the east and in the west, and in the north, and in the south, and in the islands of the sea, that they shall write the words which I speak unto them; for out of the books which shall be written I will judge the world, every man according to their works, according to that which is written. For behold, I shall speak unto the Jews and they shall write it; and I shall also speak unto the Nephites and they shall write it; and I shall also speak unto the other tribes of the house of Israel, which I have led away, and they shall write it; and I shall also speak unto all nations of the earth and they shall write it. And it shall come to pass that the Jews shall have the words of the Nephites, and the Nephites shall have the words of the Jews; and the Nephites and the Jews shall have the words of the lost tribes of Israel; and the lost tribes of Israel shall have the words of the Nephites and the Jews. And it shall come to pass that my people, which are of the house of Israel, shall be gathered home unto the lands of their possessions; and my word also shall be gathered in one. And I will show unto them that fight against my word and against my people, who are of the house of Israel, that I am God, and that I covenanted with Abraham that I would remember his seed forever." (2 Nephi 29: 10-14.)
The "lost tribes of Israel" are plural. However many the number may be, each kept records and they are to come into our possession at some point in fulfillment of this prophetic promise.
All of this was foreseen by Zenos even before Isaiah. Zenos tells us the lost tribes of Israel will be spread all about, into the "nethermost" parts of the earth: "And these will I place in the nethermost part of my vineyard, whithersoever I will, it mattereth not unto thee; and I do it that I may preserve unto myself the natural branches of the tree; and also, that I may lay up fruit thereof against the season, unto myself; for it grieveth me that I should lose this tree and the fruit thereof. And it came to pass that the Lord of the vineyard went his way, and hid the natural branches of the tame olive-tree in the nethermost parts of the vineyard, some in one and some in another, according to his will and pleasure." (Jacob 5: 13-14.)
Where is "nethermost?" How many were there?
When Christ informed the Nephites of His post-resurrection ministry, He informed them He would be visiting the various Israelite people: "But now I go unto the Father, and also to show myself unto the lost tribes of Israel, for they are not lost unto the Father, for he knoweth whither he hath taken them." (3 Nephi 17: 4.) He visited the Nephites. They were an organized body, led by prophets, expecting His birth and death. There were other organized believers who also looked for His coming. What their prophets told them, and how they understood His ministry will be in their records. What He taught them when He visited with them after His resurrection will also be in their records. It is likely to mirror the Nephite experience and record. However, it is undoubtedly true that we will again learn how involved a Redeemer He has been. Should we already realize that from what we've been given? We ought to welcome His direct ministry among us. Somehow we find His intimate involvement hard to comprehend. We think, if someone should acknowledge they have seen Him, that such a person is somehow special, different, or unique. It ought to be commonplace.
In the unfolding ministry of the Lord, the Jews were the first, but will be the last, to receive again His ministry. The gentiles have been given the Gospel. The remnant will be receiving it from them - soon.