We answer two open questions by (Gruber, Holzer, Kutrib, 2009) on the state-complexity of representing sub-or superword closures of context-free grammars (CFGs): (1) We prove a (tight) upper bound of 2 O(n) on the size of nondeterministic finite automata (NFAs) representing the subword closure of a CFG of size n. (2) We present a family of CFGs for which the minimal deterministic finite automata representing their subword closure matches the upper-bound of 2 2 O(n) following from (1). Furthermore, we prove that the inequivalence problem for NFAs representing sub-or superword-closed languages is only NP-complete as opposed to PSPACE-complete for general NFAs. Finally, we extend our results into an approximation method to attack inequivalence problems for CFGs.This work was partially funded by the DFG project "Polynomial Systems on Semirings: Foundations, Algorithms, Applications".