Someone on Facebook told me why it’s TK – those two letters are not consecutive in any English words, so you can use the ctrl + F function in word to see what’s still To Come, or TK! If you put TC, you’d come up with every word with “TC” In it! but TK allows you to easily search for what’s still coming in the manuscripts – for example, Acknowledgments / Dedication TK, Maps TK, etc!
Jane's Lessons Learned 
lol that was fast!!
Someone on Facebook told me why it’s TK – those two letters are not consecutive in any English words, so you can use the ctrl + F function in word to see what’s still To Come, or TK! If you put TC, you’d come up with every word with “TC” In it! but TK allows you to easily search for what’s still coming in the manuscripts – for example, Acknowledgments / Dedication TK, Maps TK, etc!
I was just wondering what the heck that stood for in your Christmas list… glad to have the mystery solved!