All you needed to say is "no true Scotsman". We could have filled in the rest.
You are misapplying the NTS fallacy.
For the NTS fallacy to exist, "no true" something,
something true must first exist along with the definitions of what is "false" and what is "true". The NTS fallacy includes the axiom:
True things exist and false things exist.
These are called by we Christians
absolutes, and are used to demonstrate that immaterial absolutes (truth, falsity, God, spirit, math, logic, love, justice et al) exist. Thus I encourage atheists never to invoke the NTS fallacy, for it is based on axiomatic truths that immaterial realities exist.
Further, since Jesus Christ said "you must be born again to be a Christian and follow me," I should think that HE is entitled to say some true Christians exist, and what determines them to exist, i.e. being truly born again. After all, atheists LOVE to say Jesus was the first one to espouse Christianity but the NT writers messed it up.
Can my parents tell me my sister and I are their sole two surviving children without my invoking the NTS fallacy?
Do you invoke the NTS fallacy when your espoused or spouse says, "You don't truly love me . . ."?
Jesus Christ said you and I go to Hell apart from being born again. Why are you reluctant to allow me to accept His axiomatic definition, please?
PS. If you truly (pardon the axiomatic pun) wish to deny my definition set, YOU are saying
you define the only true definition set between you and I, and are therefore guilty of the NTS error.