Comparing a topic's full related vocabulary against what your existing content actually covers is a reliable way to spot genuine gaps worth filling.
List the Related Terms a Comprehensive Treatment Should Include
Generating a thorough related-term list gives you a benchmark for what full topic coverage would actually look like.
Check Your Existing Content Against That List
Reviewing your current pages against the related-term list reveals concepts you haven't addressed anywhere on your site.
Prioritize Gaps by Relevance, Not Just Existence
A missing related concept that's central to your business deserves more urgency than one that's only tangentially connected.
Next step: Use the LSI Tool to build the related-term benchmark you'll compare your existing content against.