This precedent has been authored by Ilija Vickovich, Lecturer, Macquarie Law School and updated by Dr. Gordon Hughes, Principal, Davies Collison Cave Law.
If a contract is to be signed in counterparts, a clause is often inserted to clarify that each counterpart is deemed an original and together they constitute one instrument. The absence of a counterparts clause is unlikely to invalidate an agreement that the parties execute by separate counterparts. However, the inclusion of a boilerplate provision to that effect generally prevents a party from claiming that an agreement is not binding because there is no single document which incorporates the signatures of all the parties.
Consider carefully whether this clause is appropriate to your client's circumstances, eg whether it is preferred to have one document signed by all parties if there is adequate time.