TBH I find it hard to believe the disc is missing. It does look 1960s which makes it imperial cable. They would be headed sleeves that pass through holes in the disc and the disc would be paxolin. That is why there are no bulges in the sleeves nor a rigidly parallel approach, and why the small area between the sleeves that is not plastered with compound looks brown rather than black.
I can see crimp marks too. One would have to be remarkably absent minded and unobservant to crimp a pot without a disc in. Especially with headed sleeves which you have to pull against the inside of the disc before crimping, which would just pull off without it.
My money is on it being correct but smothered in compound. But if the disc really is missing, no it's not OK. The slightest movement could cause a short, and it's probably not sealed so the IR will be very low.