The present work concerns the use of past reference and the possible connection between verticalization and syntactic complexity in advanced Italian interlanguage in dialogues with Swedish university students. Although the NNSs' (nonnative speakers) have reached a certain syntactic complexity and refer to the past in a way similar to that of native speakers of the target language, their fluency of speech is less advanced. The students therefore recur to scaffolding and verticalize their information about past events, relying on the proficient interlocutor's interaction. It is proposed that the above mentioned discrepancy might be due to different language processing skills utilized. Native speakers have access to procedural knowledge that is required in quick speech, while the acquisitional stages seem to use knowledge that is stored in long-term memory, that is declarative knowledge. Through exposure to language the NNSs' access to on-line speech production becomes more rapid and the procedural knowledge increases. Consequently it is important to sort out different language skills when defining the advanced levels.