Metadata provides a higher-level description of digital library resources and serves as a searchable record for browsing and accessing digital library content. However, manually assigning metadata is a resource-consuming task for which Natural Language Processing (NLP) can provide a solution. This poster coalesces the findings from research and development accomplished across two multi-year digital library metadata generation and evaluation projects and suggests how the lessons learned might benefit digital libraries with the need for high-quality, but efficient metadata assignment for their resources.