It's a difficult question - the unfinished books one.
I think that books that you've made a genuine attempt to read - just for your own interest - but given up on because you didn't find them interesting enough, don't count. The reason for giving up could be that they were badly written, or the plot or subject weren't interesting to you.
But books that you've leafed through, maybe read the introduction or first chapter, and then put to one side because you're too busy, or you have another more interesting book that "you want to read first", or similar, do count. Any book which you put down with some vague idea of coming back to continue later (perhaps much later) definitely qualifies.
And books that you "ought to read", as part of a study you've been assigned by your school, or employer, or your own opinion of "this would be good for me", also count. Even though you may find the book boring, if you feel that you should be reading it if you only had the will power, then it definitely qualifies as tsundoku.
And, of course, books that you've bought, but not even looked through yet, qualify as tsundoku after some passage of time, which I shall arbitrarily set at three months. If you buy more than three months worth of reading matter at the same time, then you're probably already guilty of tsundoku, and you certainly are if you then go on to buy extra books while there are still several previously bought books in your queue.
That's my ruling
Now, who's going to go first?