PB 2 Howards Men

[Ole Boe]

From the index:
"The Scenario Defender and Attacker both exist or neither does; a scenario cannot have one without having the other."

You're only quoting a part of the relevant text. The same index entry also says:
"...while facing an opposing side that enters wholly from offboard. This latter side is termed the Scenario Attack."

Since the attacker in this scenario is not entering wholly form offboard, there is no Scenario Attacker, according to the index.

If an SSR states that there is a scenario Defender then said SSR _MUST_ also state that no Attacker is required/allowed...otherwise there is an Attacker...regardless of what "Perry Sez".

This is partly true at best. I agree that said SSR really should state that there is no SA. But it is not true that it otherwise automatically is an SA.
One one hand there is your quote, indicating that there is a SA, but there is also my quote indicating that there is no SA - making the answer impossible to answer. So the Perry sez. is a clarification to an ambigious question, not a change to a clear answer.

There should be official errata to clarify this though.

IOW, this requires an errata not just a Q&A.