Vlad I think the sentence "redacted for privacy" (**) is pretty much the default used when the domain registrar is applying the whois protection service. Filtering this specific sentence should be already enough for most of domains.
'''2.2. For fields that Sections 2.3 and 2.4 of this Appendix requires to be "redacted", Registrar and Registry Operator MUST provide in the value section of the redacted field text substantially similar to the following: "REDACTED FOR PRIVACY".'''
** Namecheap seems to use "Redacted for Privacy Purposes", but still, a simple check with the string should be enough