=UNIQUE(array) returns each distinct value once, in the order it first appears. You type it in one cell and the result spills into the cells below, as many as it needs. A blue border shows the spill range; the formula lives only in the first cell.
Because the result is a formula, it updates when the data changes: add an order from a new region and the list grows by itself.
Two optional arguments: by_col (TRUE compares columns instead of rows) and exactly_once (TRUE returns only values that appear exactly once). Wrap UNIQUE in COUNTA to count distinct values, or in SORT to list them alphabetically.
If anything is in the way of the spill range, the formula shows #SPILL!. Clear the cells it needs and the list appears.