Hot take: I billed 3 years of client SEO work under the wrong property in Google Search Console
Found out when a Denver client asked why her traffic reports never matched her actual sales, and it turns out I had the http and https versions split the whole time, so anyone else ever mix up their GSC properties like this?
Did the same thing back in 2019, except mine was www versus non-www and I didn't catch it for almost a year. Your client's lucky you found it before things got even more confusing.