Apparently your subsequent message answered my question. The total basis of the 3 lots is $2,100 before the distribution. Therefore, the basis of each lot before the distribution is $700 and after the $1,500 distribution is $200.
Several messgaes discuss how to make up for a negative basis or the effect of a negative basis at death. The tax answer appears clear: there can be no negative basis. This represents prior unreported capital gains