Assuming states act in a certain way under the belief that what they are doing is legal or legally required and other states do not object or allow the state to act that way , could this be evidence of subsequent agreement in the context of treaty interpretation or customary international law

Edit; one thing I'm curious about is that does this mean that there's no such thing as Ignorantia juris non excusat when an international treaty law isn't clear or interpreted by an authoritative source ?