wrote:
I agree with everything you just wrote. But, you have not addressed
my question. In what way does/can following the glideslope from 2000
to 1800 feet at SCK violate the regulatory implications of the SCK
ILS's 8260-3?

In the specifics cited for Stockton there is no issue of legality. My
understanding was that the CFII in question was making a general
statement about the limitations of the G/S prior to the PFAF; that is,
it is advisory only. Although using it as advisory at Stockton and
using 1800 as the floor prior to the PFAF would be both legal and
permissiable technique, it will not work where there are intervening
stepdown fixes between the point at which the approach clearance is
received and the PFAF.

It is also permissible technique to disregard the G/S and simply drive
it down to 1,800 to intercept the G/S from below, assuming there is
sufficient distance to do that.

I surmised that the CFI was thinking in global terms, and failed to
provide a complete explanation. Then again, my understanding about what
was (in) the CFI's mind is fragile at best.

In general terms: it is not legal to use the G/S as primary prior to the
PFAF. That is an important concept for the pilot to understand. It has
been proven more than once that a lot of air carrier pilots don't
understand it.