I don’t count them as completed because I didn’t complete them. Yes, I track books I DNF but I am honest about not having finished them. They don’t count towards my yearly reading goals and they don’t count towards any of my stats besides the DNF tracker. Saying “I feel like if you actively decide not to finish you’ve already completed it in some way” is just lying to yourself and anyone who might care.
Personally: The Pendragon series of YA novels. I poured my spending money into that series and even skipped school of the day Soldiers of Halla was released. My English teacher at the time was also really plugged in to YA literature at the time, so she knew exactly why I wasn’t in school and the first thing she asked me the next day was for my thoughts on the book.