Surveying, initial surveying, measurement, land surveying, stakeout, resurvey. Interesting how much is measured in a single thread.
Let's start with the large meadow. This was divided into many small parcels in the cadastre through subdivision surveying, which, according to your descriptions, the sellers commissioned, and the land register sheet was divided into many land register sheets. Under certain conditions, which are obviously present here, the marking of the boundaries can be postponed. However, boundary marking is mandatorily part of subdivision surveying, at least in NRW.
§20 VermKatG:
... (3) Boundary marking shall be postponed if and to the extent that property boundaries cannot be permanently marked temporarily, for example due to construction works. The respective surveying authority is obliged to carry out the boundary marking after the obstacles have ceased.
If nothing is stated in your purchase contract about cost assumption for the surveying, the seller has already paid for the subdivision surveying and thus also for the boundary marking. If you do not need to know exactly where the boundary runs at the moment, you can wait until the surveying authority carries out the boundary marking.
If you are smart, you find out which surveying authority is responsible and commission the building stakeout there. The fee schedule allows room for discounts when multiple surveys (here: boundary marking and building stakeout) for one property or several nearby properties are carried out simultaneously, which the surveying authority hopefully passes on to the customer.