This study aims to account for the variation in aspect choices in factual imperfective contexts in Polish, Czech, and Russian. A series of online questionnaires were conducted wherein the native speakers of the tested languages were asked to fill in the missing verbs for two types of existential contexts (neutral and resultative) and four types of presuppositional factual contexts (weakly and strongly resultative with a focus on the initiator or the result state of the past event). We show that neutral existential factual contexts generally elicited significantly more imperfective choices than resultative existential factual contexts. Additionally, there was a trend towards a higher usage of imperfective in weakly resultative presuppositional contexts as compared to strongly resultative presuppositional contexts, suggesting that the less emphasis is placed on the result state the more likely the choice of imperfective aspect is for the expression of the temporal indefiniteness of factual contexts. Russian showed a significantly higher proportion of imperfective uses than Polish and Czech, with Czech being intermediate. We argue that these observations result from the fact that in all types of factual contexts (both existential and presuppositional) there is an interaction between two types of TEMPORAL (IN)DEFINITENESS of the past event: (i) temporal (in)definiteness at the micro-level (first phase syntax-vP) (depending on the position of the time variable within the temporal event of the past complex event) and (ii) (in)definiteness of the past event at the macro-level (second phase syntax–AspP and TP) (related to the position of the past event relative to the utterance time). We show that both discourse-level information and verb-level information interact in determining these two types of (in)definiteness, and they do it differently in Polish, Czech, and Russian.