It depends on the order of construction.
If you construct via properties without ALSO noting whether it exists or does not exist, you can justify the potential existence of unicorns by pointing to the properties of Rhinos and noting similarities.
But if you construct noting that by definition unicorns do not exist whereas rhinos do exist, no amount of property adding can construct an existing unicorn. It can only construct an imaginary unicorn which could be on par with an imaginary rhino but not with a rhino-defined-as-existing