Is the property size correctly stated in the exposé?

Not at all.

A fully owned plot plus ownership share in a private road and an ownership unit consisting of special and common use in a WEG are definitely an apples-to-oranges comparison.

It's really just the number of affected parties, 20 instead of 3 or 2. A private road brings more obligations than benefits. With a public road, the municipality is responsible for road maintenance (including clearing and gritting). With a privately shared road, the parties are responsible, but one party cannot dispose of this access because the right of way must be observed.
If you now proportionally add up the square meters in the exposé, as an interested party you always have to ask whether it is a public building area or a private one, because the private party can simply make the land areas appear larger than they actually are. They can, for example, proportionally add the development road.

The fact is, the total offer has its price, and if it is marketable, then there is no need to dream of a discount. Nor about the mimimi reference to the price indication regulation that meat must be priced per kilo and fruit per hundred grams. The price is and remains in total "X". What advantage would you see in having "455/511 X + 46/511 X" individually stated on the receipt?

because the private party can simply make the plot areas appear larger than they are. He can proportionally include the access road.

P.S.: Be glad that the plot was developed privately and the dead-end street was economically planned. The municipality would have wasted a flat 20% on public areas during the plot development in the land readjustment procedure. Then there would now be a helicopter landing pad for turning the garbage truck, and visitor parking spaces for parking completely unknown motorhomes.