The underlying issue was my lack of understanding of the double arrow.
----> is equal to <----->
I was merely breaking down what is described on p. 305 in more basic terms.
obviously it is not used in this case but yes, the use of both necessary and sufficient condition indicators before a condition creates a double arrow (ie two arrows put together).
like "if and only if"
when/if = sufficient condition indicator
only when/only if = necessary condition indicator
so "if and only if" or "when and only when" creates two setups but it is easier to do it with a double. p.305 did not explain it well enough for me at first glance.
BTW:"only when" is not on the list of necessary condition indicators... but obviously is one.