Hello Austria-Czech SIG:

My thanks to those who replied to my query. The consensus is that the
Familianten books were not dated and were constructed or copied over a
number of years. As such, they probably cannot be considered primary
genealogical records. And, the recording of a living parent's name as
"unknown" has baffled others. One could surmise that it was simply
"unknown" to the transcriber who (lacking a telephone and email) did
not make further inquiry.

Dave Bernard, Sherborn, MA