finding much of an answer online. I'm not even 100% sure an EX-TL is an official trim designation.

Backstory is I purchased my daughter a '16 Civic that was listed by a used car dealer as an EX-L. When I went to add it to my insurance, when I entered the VIN, my insurance added it to our policy and listed it as an EX-TL.

When you look at Honda's official listing of their trims (LINK), it doesn't show anything called an EX-TL.  But if you go down to the bottom of the page in footnote 24, it refers to the EX-TL there.

Does anyone have any insight at all?