Dave Newt wrote:

Sometimes when I ask for Hertford East to Bounday Zone 3, my ticket says
"Boundary Zone 3". Other times it says "Seven Sisters", "Tottenham
Hale", "Northumberland Park" or "White Hart Lane". I assume it's a case
of the ticket seller either knowing how to issue BZ tickets or, if they
don't, just guessing what the appropriate destination should be.

It *should* say one of Bowes Park, White Hart Lane or Northumberland
Park, depending on what route you're taking. Tickets must NOT be sold TO
Boundary Zones, as otherwise it all gets very confusing. (Boundary Zone
3 heading outward, becomes Boundary Zone *4* heading inbound)

In fact, last time I did it in the opposite direction, and asked for
"BZ3 to Hertford East", the ticket seller at Tottenham Hale thought for
a millisecond, then asked me "How much do you normally pay for that
then?" I replied, "Oh, about £6.20 I think", and he issued me with an
LUL Extension ticket for £6.20, i.e. no destination of any sort printed
on it.

Is this because they don't know, or because it involves pressing too
many buttons, or is there actually a good reason for it?

It's more likely because the LU ticket machines aren't *that*
sophisticated. Though they *can* show certain NR destinations.

Cheers,

Barry