@conejo23 - There aren't many different criteria that an Evernote user can base his structure scheme on. Examples are "Who", "What", "When", "Where", "Type". Given the issue you have raised, I would add "Purpose" to the list. When it comes to your 2016 Taxes, it seems to me that you chosen to define a Notebook around the "purpose" of the documents in your Evernote database and to use Tags to define the "Type" of documents (W2, K1). That's all well and good. I suspect it will work just fine for you.
I believe what DTLow was pointing out to you was essentially the reverse. That is, define your Notebooks around the "Type" of documents (receipts, and insurance policies, which you have already done) and define your Tags around the "Purpose" of the document (and documents commonly have multiple purposes). As I look at the names of my Notebooks, most of them conform to this structural scheme. One reason I like this structure is that the "Type" of a document isn't likely to ever change, while when I either create or obtain a new document (or, in general, information), I can't always anticipate the future "purposes" I might have for it. - - - In addition, as a user's Evernote database grows, I think this kind of structural scheme will be more effective.
And, of course, there is on other basic scheme. That is: 1 Notebook, no Tags, and add/use keywords with the title or body of the Notes.
But again, go with what you believe is going to work well for you with your 2016 Taxes. - - - My suggesting would be that you (and any Evernote user) sit down and spend 10-15 minutes and seriously think about what scheme you will use for Notebooks and Tags. Then, adhere to it as best as you can for at least a few weeks. Over time (months to years), I sense that a fair amount of Evernote users change their scheme as they become more aware of the kinds of material they have been putting into Evernote. - - - And it's not a big deal to change a scheme. One of the great features of Evernote is that it will allow you to change the Notebook or Tag of a large batch of Notes all at one time.