@wikipathways still has a good number (200 to 250) pathways that do not have a single reference (which does not mean no references were used): https://www.wikipathways.org/wikipathways-collection/index2#at-least-one-reference
I think we need some gamification here... a few tools that take the GPML or RDF and suggest a relevant lit reference, which then gets posted to this issue tracker (https://github.com/wikipathways/pathway-curation-tasks/issues), listing the WPID and PMID, PMCID, or DOI, and ideally the graphID of the DataNode or Interaction