Others may be able to give you steps to work with the
indexing, but I just wanted to share what I do.
If a topic should come up in a search even though the keyword
is not included in the topic, I add the keyword - literally.
At the bottom of the topic, I add:
Keywords: W-2, W2, tax forms, NEBS
etc - whatever associations will help find the topic.
Easy to maintain - clients often will let me know which
keywords to add.