No its not too late - but you should understand that the FA item list has limited functions in QBdt Pro. Its actually designed to be used as part of the "FA Asset Manager" system that is part of the QB Premiere & Enterprise versions.
To setup an FA item retroactively, you need to first create the item, then edit the prior bill/cheque which purchased the asset and change it from an 'account' type entry to an 'item' entry - with the same value.