At what point does one have 30% degredation?
The 30% applies to the newer cars and won't apply to your car. The U.S. warranty for a "6 year old car" like yours is included here:
Download and save.
No mention of 30%. But, you have Elon Musk's own words, when he said "If something goes wrong, it is therefore our fault, not yours", described under Creating the World’s Best Service and Warranty Program
But will 185.5 miles be a trigger for a battery swap?
I don't think so. Our warranty didn't have a range loss phrase in it; that phrase is more recent. Technically, without a clear sign of some failure, they don't have to replace it at all.
From what I've read in this forum, Tesla won't accept a customer's data extracted from their own car. Customers are forced to rely on Tesla alone to read and interpret their car's faults as they see fit.
It might help to notice what @DJRas was told by a Tesla Service Center regarding the Tesla's secretly kept "Fleet-wide average":
Sudden Loss Of Range With 2019.16.x Software