In this paper, we discuss the fact that not only adverbially quantified sentences with singular indefinites or bare plurals but also ones containing plural definites show Quantificational Variability Effects, that is, they receive readings according to which the quantificational force of the respective DP seems to depend on the quantificational force of the Q-adverb. We show that if the Q-adverb is a frequency adverb like usually, there is strong evidence that QVEs come about as indirect effects of a quantification over (...) situations. This conclusion is based on the fact that in such cases the availability of QVEs is constrained in ways that have no parallel in sentences containing adverbs of quantity like for the most part or quantificational DPs instead of frequency adverbs. We show that these constraints can be derived from plausible assumptions about how the situations to be quantified over are constrained: they have to be located in time on the basis of the most specific locally available information, and their running times are not allowed to overlap. (shrink)