You can take their word for it, but yes, that is unreliable. I don't typically have an internal narrative, it takes effort. I sometimes have internal dialogue to think through an issue by taking various sides of it. Usually it is quiet in there. Or there is music playing. This is the most replies I have ever received. I think I touched a nerve by suggesting to people they do not exist.

I get you somewhat, but remember, you do not have another consciousness to compare with your own; it could be that what others call an internal narrative is exactly what you are experiencing; it just that they choose to describe it differently from you