I doubt it. Unless there's evidence that the property ever included 21 air-conditioning units, the courts would likely view it as an error subject to rectification. See under heading "Unilateral mistake" here: http://www.claytonutz.com/publications/newsletters/projects_insights/20110921/rectification_what_to_do_when_your_contract_is_not_your_contract.pageLegally he could ask for the 21 units
Edit: I am not a lawyer and all that...
Last edited: