Historical analysis: Verse 2 clarifies some very important parts of the provenance of the record we now have. The first and most obvious statement is that Nephi has created two sets of plates. The second, and less obvious indication, is that the two sets of plates pertain to two different time periods. The third piece of information, which should be obvious, but which should nevertheless be made absolutely explicit, is that we are reading the second (and later) of the two accounts.
The immediate reference of 1 Nephi 18:25-1 Nephi 19:1 is therefore probably the first record, which we know as the large plates of Nephi. The record referred to in 1 Nephi 19:2 is what we know as the small plates of Nephi.
Verse 2 also clarifies some of the relationship between the two sets of plates. Nephi tells us that when he created the first set of plates he was unaware that he would be creating a second set. He indicates that for this reasons the "history" of their journey is more completely told on the first set of plates. Thus we should understand that by the time Nephi began writing the record that we read he has already covered this material, and in greater depth, on a different set of plates. While it isn't specifically stated, it should be obvious that the other set of plates was also in Nephi's possession, and his confusion as to why he should create a second set of plates would have been increased by the ready availability of the first set.
The nature of the textual differences between the two sets of plates is set forth in the following verses 3 - 5.