I contacted Marketo Support about a potential bug and learned some helpful info that I thought the community could benefit from...
I set up a Subscription to a Smart List and edited the columns to include info about "Last Interesting Moments." These new columns didn't show up when I went to download the report in the email notification. I learned from Support that some fields require a Marketo ID as an additional column in order to be exported. There isn't a list of all fields that need the ID column. To be on the safe side, include ID as a column for Smart List Subscriptions.
Also, I realized that if you just go into the Leads tab of your smart list and edit the default view to include more columns, that won't cause them to appear in your smart list subscription that is sent to you. I was confused for a minute that I wasn't seeing a certain field that I added, while all the others were there. You have to go to Marketing Activities --> Subscriptions --> click Edit under Report Columns. Although I had added it when I edited the default view, it wasn't included in the actual report columns, so I added it again here.