Abstract. We investigate closed, symmetric L 2 (R n )-realizations H of Schrö-dinger-type operators (−∆ + V ) ↾ C ∞ 0 (R n \Σ) whose potential coefficient V has a countable number of well-separated singularities on compact sets Σ j , j ∈ J, of n-dimensional Lebesgue measure zero, with J ⊆ N an index set and Σ = j∈J Σ j . We show that the defect, def(H), of H can be computed in terms of the individual defects, def(with potential coefficient V j localized around the singularity Σ j , j ∈ J, where V = j∈J V j . In particular, we proveincluding the possibility that one, and hence both sides equal ∞. We first develop an abstract approach to the question of decoupling of deficiency indices and then apply it to the concrete case of Schrödinger-type operators in L 2 (R n ).Moreover, we also show how operator (and form) bounds for V relative to H 0 = −∆ ↾ H 2 (R n ) can be estimated in terms of the operator (and form) bounds of V j , j ∈ J, relative to H 0 . Again, we first prove an abstract result and then show its applicability to Schrödinger-type operators in L 2 (R n ).Extensions to second-order (locally uniformly) elliptic differential operators on R n with a possibly strongly singular potential coefficient are treated as well.