Why Date.parse function is parsing “Lender Series Email 2” string but not “BrokerVIPemail5 2” string?

How Date.parse function parse its value.

Date.parse("BrokerVIPemail5 2") // NaN
Date.parse("Lender Series Email 2") // 980965800000

Problem is i don’t know whether string is random string or date.
any solution to check if value is of date string?

Any response would be helpful

Thanks in Advanced.