Originally Posted by SamOF

Not to pile on, but you weren't seeing Z availability on the KLM flights—you were seeing Z availability on the Delta flights. It seems possible to me that the second agent was making the same mistake, and her confusing explanation was trying to say that you need Z on the KL numbers, not the DL numbers.

There's no way to check this on Delta.com. Expertflyer has the info you need, as does ITA Matrix if there is a Z fare filed in the market.