Official means the information we got from Runewaker and is confirmed and documented when the Patch is published. Inofficial means stuff you come across after a patch and think it has changed but was not mentioned in patch notes, which means we need to look into it and get it confirmed if it is indeed an undocumented change that was not mentioned in the patch notes we received or rather an unintended change or bug that needs further adjustments

Inofficial and Unofficial both is possible spelling, I take it inofficial is a more British version compared to unofficial being more American version (ref.
http://www.dict.cc/?s=inofficial and
http://www.dict.cc/?s=unofficial as example)