Large-scale digital libraries such as the HathiTrust contain massive quantities of content combined from heterogeneous collections, with consequential challenges in providing mechanisms for discovery, unified access, and analysis. The HathiTrust Research Center has proposed 'worksets' as a solution for users to conduct their research into the 15 million volumes of HathiTrust content; however existing models of users' information-seeking behaviour, which might otherwise inform workset development, were established before digital library resources existed at such a scale. We examine whether these information-seeking models can sufficiently articulate the emergent user activities of scholarly investigation as perceived during the creation of worksets. We demonstrate that a combination of established models by Bates, Ellis, and Wilson can accommodate many aspects of information seeking in large-scale digital libraries at a broad, conceptual, level. We go on to identify the supplemental information-seeking strategies necessary to specifically describe several workset creation exemplars. Finally, we propose complementary additions to the existing models: we classify strategies as instances of querying, browsing, and contribution. Similarly we introduce a notion of scope according to the interaction of a strategy with content, content-derived metadata, or contextual metadata. Considering the scope and modality of new and existing strategies within the composite model allows us to better express - and so aid our understanding of - information-seeking behaviour within large-scale digital libraries.