“therefore I make a record of my proceedings in my days”
Sometimes we assume that the book of 1 Nephi is like a journal – that Nephi kept it as he went along. Maybe that’s the case for the other plates he kept, I don’t know, but with the version we have access to, Nephi wrote his record 30 years after Lehi’s family left Jerusalem, and well after the time they arrived in the Promised Land. (see 1 Nephi 19:1-5 / 2 Nephi 5:28-31)
1 Nephi 19:1-5
4 Wherefore, I, Nephi, did make a record upon the other plates, which gives an account, or which gives a greater account of the wars and contentions and destructions of my people. And this have I done, and commanded my people what they should do after I was gone; and that these plates should be handed down from one generation to another, or from one prophet to another, until further commandments of the Lord.
5 And an account of my making these plates shall be given hereafter; and then, behold, I proceed according to that which I have spoken; and this I do that the more sacred things may be kept for the knowledge of my people.
2 Nephi 5:28-31
28 *And thirty years had passed away from the time we left Jerusalem.
29 And I, Nephi, had kept the records upon my plates, which I had made, of my people thus far.
30 And it came to pass that the Lord God said unto me: Make other plates; and thou shalt engraven many things upon them which are good in my sight, for the profit of thy people.
31 Wherefore, I, Nephi, to be obedient to the commandments of the Lord, went and made these plates upon which I have engraven these things.
32 And I engraved that which is pleasing unto God. And if my people are pleased with the things of God they will be pleased with mine engravings which are upon these plates.
33 And if my people desire to know the more particular part of the history of my people they must search mine other plates.
34 And it sufficeth me to say that *forty years had passed away, and we had already had wars and contentions with our brethren.
Why does that matter, you ask? Well, I suppose it doesn’t, really. I just thought that was kind of cool.