FROM " . TABLE_ORDERS_STATUS . " os, " . TABLE_ORDERS_STATUS_HISTORY . " osh
In the context of the query you quoted,
os is a shortname/alias for TABLE_ORDERS_STATUS
osh is an alias for TABLE_ORDERS_STATUS_HISTORY

Thus, osh.tracking_number would refer to a field named "tracking_number" in the orders_status_history table.

And your latest error message indicates that no such field exists in that table.