Here in 2 Nephi 29:14, Oliver Cowdery initially wrote “the lands of their possession”, but then almost immediately he corrected the number of possession by inserting inline a plural s (there is no change in the level of ink flow). The original manuscript is not extant here but probably read in the plural.
The common Book of Mormon expression for this construction has both land and possession in the plural (that is, “the lands of one’s possessions”). Based on the earliest textual sources, there are five other examples of the double plural construction:
Over time the text has occasionally replaced either lands or possessions with the singular form. In Alma 50:12, the 1830 typesetter replaced the second instance of possessions with possession but left the first instance (which shows that his change to the singular was probably accidental). On the other hand, in Alma 54:6, the editors for the 1920 LDS edition consciously replaced lands with land, even though the preceding phrase reads in the plural (“into your own lands”). The reason for the change (which is explicitly marked in the 1920 committee copy) is because the following relative clause has land in the singular (“which is the land of Nephi”). In both cases, as in all the others listed above, the original text had both nouns in the plural (“the lands of one’s possessions”). It should also be pointed out that there has been a tendency in the text to replace the plural lands in “the lands of one’s inheritance” with the singular land (thus “the land of one’s inheritance”). For discussion of those instances, see under 2 Nephi 9:2 and 2 Nephi 25:11.
In the original text, the double plural construction is the most frequent form of the phrase “the land(s) of one’s possession(s)”. But there are two examples for which the earliest text supports singular rather than plural forms:
The original manuscript is not extant for either of these two passages, so one wonders if these might involve an error in number, especially given the dominance of “the lands of one’s possessions” as well as the clear tendency to replace the plurals lands and possessions with singulars. It is also interesting to note that in the first of these two examples (Helaman 5:52), both the 1874 RLDS edition and the 1906 LDS large-print edition replaced the singular possession with its plural, thus ending up with the dominant construction, “the lands of one’s possessions”. For further discussion of these two exceptional cases, see under Helaman 5:52 and Helaman 7:22.
Summary: Maintain in 2 Nephi 29:14 the double plural construction “the lands of their possessions”, the corrected reading in 𝓟; similarly, this double plural usage should be restored in Alma 50:12 (the second occurrence) and in Alma 54:6.