When Mormon states that "I made this record out of the plates of Nephi" (Mormon 6:6), he seems to be refering to his abridgment of the Large Plates of Nephi (the Plates of Mormon). Even if our assumption is correct, however, it is hard to tell by Mormon's words whether he was just completing a record already started (maybe during his 13 year interval of standing as an "idle witness") or if he made his abridgment after he had gathered in his people and before the final battles (Mormon 6:6).
In view of the many records that Mormon used as source material (Helaman 3:13, Words of Mormon 1:3-5, Moroni 9:23), if Mormon attempted to make his abridgement after the gathering was completed (as the order of the text seems to imply, then in less than a year he would have needed to abridge the messages contained in what amounted to over 100 times the material contained within our present Book of Mormon (3 Nephi 5:8). Perhaps Mormon did much of his abridging previously during the 13 year interval in which he stood as an "idle witness." Or perhaps Mormon made his abridgement during the four years of gathering. Whatever the case, Mormon "made this record" by first abridging the Large Plates. He then apparently added the small plates of Nephi (Words of Mormon 1:5). Next, Mormon attached to the small plates of Nephi an explanatory note detailing what the Small Plates were (Words of Mormon 1:1-7). Mormon then proceeded to "finish" his record (Words of Mormon 1:9) by first completing his Words of Mormon with a historical summary (Words of Mormon 1:10-18) of king Benjamin's reign, designed to bridge from where the message of the small plates stopped to the proper historical spot in Mormon's abridgment of the Large Plates. Finally, Mormon filled in the Title Page to his "record," and "gave" Moroni the responsibility to complete what he had started if he (Mormon) were not to survive the last battle (Mormon 8:1). Thus, Mormon's statement in the year 385 that he "made this record out of the plates of Nephi" (Large and Small Plates) can be fully justified. [Alan C. Miner, Personal Notes] [See Alan C. Miner, "The Chronology and Compilation of the Writings of Mormon and Moroni"] [For alternative insights, see also the articles from the Book of Mormon Symposium #9 entitled "Why is 4 Nephi So Short?" by Steven L. Olsen, and "Mormon's Greatest Work Came After Cumorah" by Donald L. Enders, Sr.] [See Appendix B--Records]