Jul 16, 2019 - 10:00 AM
I can add a bit from my experience and will request experts to correct if there need be.
For attractions like schilthorn, even if its covered fully under the Swiss Pass, you are still expected to buy the ticket at the cable car station. When you display your swiss pass, they will provide you the ticket at no cost ( or otherwise by charging whatever is appropriate )
You will need to get the ticket because there are turnstiles at the cable car stations and you got to scan the bar code printed on the ticket to open those gates
I have not read or heard about 'sold out' instance but I would leave that for the experts to answer.