@StephenK
Remember this is Bmw we are talking about probably didn't have one from new if it wasn't ticked on the option list
Absolute base model z3 even the radio head unit was an option they only come with radio preparation which means speakers all fitted but cubby hole instead of radio.
Was the norm for bmw through 80's and 90's
Like so many z3 dont have roll over hoops and you'd think in the late 90's that would be standard safety kit
Same with airbag most zeds ( especially pre face-lift ) only have drivers side air bag even though you can get passengers and later on side bags again stuff you'd like to be standard so I'd definitely be leaning towards your zed never had a tonneau to start with.
Stephen.