The short form is that units should not be distributed at the end of the year. This is a break on how it was recorded in the past, but it makes things easier, and it's proper accounting.
In the past, both the number of units owned and unit value changed at the end of the year, after running a Distribution of Earnings. This practice started before computerized accounting programs with the accounting manual put out by NAIC for investment clubs.
The idea was to mimic mutual funds, who pay out all their earnings annually, and whose shareholders, mostly, reinvest those earnings back in the fund. Investment clubs, unlike mutual funds, do not have to pay their earnings out each year. Moreover, the members are taxed on those earnings whether paid out or not.
In an attempt to mimic mutual funds, NAIC caused additional units to be 'distributed' to each member. But then, because a member's value does not change simply because taxable income has been allocated, they were forced to make an offsetting adjustment to the unit price. In the end, members ended up with more units, which were worth less per unit, and exactly the same total value as before!
This was a needlessly confusing exercise. There were other adverse ramifications, in some cases. If the club suffered a loss for the year, units were taken away. Also, it was confusing to have the unit value of the club go down, when the club had experienced earnings for the year.