As I said, Harry did need LC in TC.

I am not sure I see why is that is true.  LC takes a lot of work and if Thomas is not in Chicago then would have provided no value.  So, I am confused why Harry needed LC.  I took the whole event to be based around the fact that he could not track Thomas with his blood.  It is not clear to me that using LC makes the spell more capable beyond providing more information and being able to track things as a spirit of sorts.  But if Thomas is in say Naperville or Joliet, then there is no value to it.

Well, I think a better way of saying that is "Why would you believe that Shagnasty had Thomas in Chicago?"  Little Chicago only matters if he is.  If he is not, the best you might know is what path was taken.  I also thought the use of LC was essentially a tracking spell in any case.  So, maybe Harry figures if he gets nothing from tracking spells at all why spend all the energy to use LC.