Considering the acquisition of past tense uses by L2 Spanish advanced learners with closely related L1s (French, Portuguese), this study attempts to identify factors associated with variability, such as negative transfer or interface integration. We report data on the acquisition, by adult L1 French and Portuguese learners at B2 and C1 CEFR levels, of Spanish tense-aspect morphology: simple and compound past (SP, CP), imperfect (IMP), progressive (PROG), and pluperfect (PLP) forms, and from a control group of European Spanish speakers' use and interpretation of these tenses. Data were collected through a film oral retell and two written interpretation tasks; the second written task (a follow-up task), was performed only by L1 French speakers. In the oral task, comparing both L1 backgrounds, negative transfer is more pervasive for the Portuguese groups. However, in the interpretation tasks, the French speakers showed greater difficulties, linked not only to L1 transfer but also to nonprototypical tense/aspect associations and pragmatically based temporal reference. The data suggest, in relation to Lardiere's (2008, 2009) Feature Reassembly Hypothesis, that both feature reassembly and interface integration are sources of variability in the acquisition of L2 interpretable features that are also present in the L1.