Amendment sought by claimants after initial closing submissions – Facts on which amendment based already known – Defendant not caught by surprise – Principles that should guide court in determining application – Scope of powers in the Registration of Titles Act (ROTA) to correct “errors” – S. 153 (ROTA) inapplicable in the circumstances as issue is validity of Title itself not the manner in which Certificate evidencing Title was obtained – Doctrine of Adverse Possession – More than 12 years unchallenged open possession – Doctrine of Proprietary Estoppel – Unconscionable for defendant to wait 8 years after a party has acted to its detriment before seeking to enforce her right