Hello Roland,
I was given this answer a few days ago (see below). So I booked the transfer on SBB both hotels came up it and the system allowed me to book it.
You can book an express luggage transfer from Interlaken to Lauterbrunnen without issues, as Lauterbrunnen is accessible by car. For Wengen, a car-free village accessible only by train or cable car, luggage transfers are typically managed through Swiss Railways (SBB). This means you can still book the transfer, as the service accounts for the unique transportation needs. For transferring from Wengen to Grindelwald Station, the SBB service handles the logistics via train. Confirm with the service provider or book directly through SBB to ensure smooth transfers.
Best Regards,
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