Not clear losses in own rear ?!

[Heldenkaiser]

I am fairly certain I have seen interdiction occur whether there were available air units left unused at the end of the turn or not.

The manual says --

"If Interdiction occurs, then an Air Strike occurs against a unit in the target hex using an air unit that is representative of the type of air unit available to the enemy side. However, this air strike does not count against the air units available by the enemy."

If an unused air unit would have to be available, wouldn't the underlined phrase just say "using an air unit available to the enemy side"?