Wills, probate, letters of administration, powers of attorney
Without further information it would seem to me that the deceased owned a piece of land that the executors were not aware about, so once they became aware of it they, as executors claimed it part of the estate to be distributed in terms of the will that the deceased left.
Obviously the land was not described in the will, or they would have known about it, so it would be included with the residual of the estate, probably, and so distributed.
To XYZ I leave the residual of my estate, or the residual of my estate should be divided equally between QRX, ABC and UVW.
If you have the description of the land perhaps you could do a title search and take a look at the ownership over the years with respect to the time of the estate distribution.