"Course of dealing," as defined in [UCC § 1-303] subsection (b), is restricted, literally, to a sequence of conduct between the parties previous to the agreement.
"[5] It is well established that a written contract may be modified by the parties' post-agreement "course of performance.
"[6] A waiver that changes the express terms of a contract can be established by evidence of a course of performance.
The policy behind this "broad doctrine of waiver" in contract law is to "prevent the waiving party from 'lull[ing] another into a false assurance that strict compliance with a contractual duty will not be required and then sue for noncompliance.'
[8] A course of performance is shown by repeated instances of the relevant conduct, not single occasions or actions.