Ask what they are waiting to put in that parcel and whether the correct cable is actually available. Holding a stocked item and waiting to source it are different problems.
I have my own missing cable argument running, and I'd want more than stocked in an email before describing it as on the way; did they identify the actual cable they propose to send?
Ask for the relationship between those references, not just whether it fits. It may be a supported replacement, but the supplier needs to identify that and your technical reviewer needs to assess it.
Keep the separate-shipping request open while they answer the technical point. You do not want them interpreting the compatibility question as agreement to wait for the whole kit again.