The former is past perfect[1], and the latter is past perfect progressive.[2] There are subtleties involved, but the most basic use case is that the former ref

The former is past perfect[1], and the latter is past perfect progressive.[2] There are subtleties involved, but the most basic use case is that the former refers to an action that took place before some point in the past (to which the sentence refers), while the latter refers to an action that was still happening at that past point. [1] https://en.wikipedia.org/wiki/Uses_of_English_verb_forms#Past_perfect https://en.wikipedia.org/wiki/Uses_of_English_verb_forms#Pas... [2] https://en.wikipedia.org/wiki/Uses_of_English_verb_forms#Past_perfect_progressive https://en.wikipedia.org/wiki/Uses_of_English_verb_forms#Pas...