I think I might have figured it out. The Volvo belt is of course correct. The Continental belt TB324 (round toothed) has the exact same teeth, pitch and length as the Volvo belt. But note that Contitech and others list the fitment as not only for later Volvo 940s and 240s, but also other engines such as 2000-2003 Hyundai Accent which may well have slightly different sprocket timing marks. I'm sure after 25 years you can forgive Contitech for possibly trying to save a dollar and combine otherwise identical products under the same part number. If they were more observant, they'd have dropped the white lines completely in order to avoid confusion, or perhaps the engineers didn't notice that the belt markings for Volvos are a mere one tooth different and someone thought they were identical in all regards.

The other possibility is a simple mixup on the production line that may have extended for many months or even years worth of stock where the white lines were incorrect for both Volvos and Hyundais. Installed properly by a trained professional mechanic where sprocket timing marks should always take precedence, it's possible no one has ever had an engine running issue and if they did, they never complained to Contitech.

No matter what the white lines on the belt or which way the belt is facing when it's mounted (it makes no difference which way), what matters most is having the sprockets properly aligned for installation and that the belt is wrapped in order to keep the non-tensioned spans fairly taught so as to preseve sprocket alignment when properly tensioned. After installation, always rotate the crank a couple of times and re-check the timing sprocket alignment marks in addition to the belt tension. The exception of course is the intermediate shaft on the later 740 and 940 B230s which have their distributors on the back of the cam and the sprocket timing mark makes no difference other than to satisfy idiots like me. I've never done the actual calculation, but it would likely take several hundred revolutions for the belt marks to line up again with the sprockets.

Now that we know this kind of thing can happen, the white line markings on all makes of timing belts should be taken as suggestions at best.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now