There can be inequivalent Legendrian knots that are isotopic as topological knots. Many inequivalent Legendrian knots can be distinguished by considering their Thurston-Bennequin invariants and rotation number, which are together known as the "classical invariants" of Legendrian knots.
Some Legendrian knots that are distinct in topology may also be identical in their isotopic form.  The distinguishing features of these knots can be determined using their Thurston-Bennequin invariants and rotation numbers, which together constitute the "classical invariants" for Legendrian knots.