Ann: 74.5 Carat Diamond Among More Large Recoveries at Lulo, page-47

An average of the remaining will only work if you first deduct the data from those you have discussed as a smaller group.
Thus the remaining cannot be 1.6, unless the average of the ones you discussed in the smaller group were also 1.6, which they were not, as their average was 27.59.
And you cannot determine the adjustment to the average, unless you know (or calculate) the original number of stones used in determining the average.

Hence refer to my reply to zippy, as I provide that rough calculation.
And then you can see why my original question of "then how small must the others be to get that average" is actually a valid (and calculable) question.