The end of Mormon's abridgment

When Mormon abridges the records and gets to the end of a book, he often writes something like "and thus ended the record of x", always in the past tense. See for instance

• Alma 44:24: "And thus ended the record of Alma, which was written upon the plates of Nephi." 

• Alma 63:17: "And thus ended the account of Alma, and Helaman his son, and also Shiblon, who was his son."

• Helaman 15:25: "And thus ended the book of Helaman, according to the record of Helaman and his sons."

In the last verse in 4th Nephi, he writes: 

And thus is the end of the record of Ammaron. 

What is noticeable about this is the shift to present tense. It is subtle, yet distinct. It makes a lot of sense because Ammaron is the last one to write on the plates before Mormon. In other words, Mormon is now done with the abridgment, so this is it, this is the end. On the other hand, if it's Joseph Smith making it all up (which I obviously don't believe), it’s just very clever!