More than a week ago, John Moon requested some additional
clarification about the distinctions between "gnostic" and
"non-gnostic" elements in GTh. My apology for the delay (see my
response to Mark Goodacre for my excuse).
The lines between what (presumably Jesus) actually taught
and the concept of Gnostic Christianity, where they (those lines)
get very shall we say fuzzy?
It would appear that some evidence exists to suggest that a pre
existed (which I believe we discussed on the list some time
the question becomes might not the original (although possibly
later) have been at least partially Gnostic.
If I comprehend correctly, I think your first question can be
restated this way:
 Are the "lines of distinction" between the "gnostic" and
"wisdom" strata always clearly defined?
No, I don't think they are always clearly defined (if I
understand Bill Arnal's HTR article, a discussion of which
initiated this thread in the first place). That is not to say
however, that there are not some "signals" that point to gnostic
characteristics. These signals include (pp.478f):
A. The presence of "gnostic mythological motifs" (e.g., 50, 101).
B. "Deliberate obscurity and use of external points of reference"
C. The presence of "named disciples" (13,21,61,114).
D. "Tendency toward the dialogue form" (13,22,60,61).
E. Word plays (18, 101).
F. Arrangement of sayings in pairs (21+22, 27+28, 50+51, 60+61,
G. Themes of:
becoming one, single or alone (11, 22, 48, 61, 114);
the end is the beginning (18, 49);
salvation as the avoidance of death (18, 61, 111);
use of the word "living" (11, 50, 101, 111);
use of the term "repose" (50, 60);
references to "light" (50, 61, 83);
the image of drinking from Jesus' mouth (13, 28, 108).
When more than one of these characteristics are present in a
single saying (and as you can see from above, this happens
frequently), it becomes most certain that it is evidence of
John's second question seems to be:
 Is it possible that the gnostic strata is original and the
sapiential strata is secondary?
Bill seems to say that the answer is "no." He offers three
A. "...in terms of the history of the tradition, this order
[wisdom to gnostic] makes most sense in its progression from
inversionary wisdom to Gnosticism."
B. "... the interpretation of the document as a whole is
controlled by the incipit and the first two sayings, directing
the reader to a 'hermeneutic of penetration' for all that
follows. It is precisely through this device that the gnostic
redaction is able to subsume and interpret the wisdom material in
line with its own perspective."
C. "...although the themes which characterize each stratum appear
to be distinct from each other, there are secondary glosses to
the wisdom material from the gnostic perspective."
It seems safe, therefore, to characterize the secondary strand as
gnostic and the primary stratum as wisdom. I also think that
John's concern that the distinctions between the two do not
always "glow in the dark" is valid. One who wishes to attend to
these distinctions is advised to read VERY carefully.
Humble Maine Woodsman