OK, so I visited TMC today in order to see if there was any more info on the range loss.... and I find Mr. Ninja expressing almost the identical situation that I am facing. He's as persistent as I am, so I'm looking forward to anything he turns up.
Let me toss this out right up front in an attempt to avoid the coming "just put it on percentage and everything will be great!" I have lost REAL range. As in the number of miles that my car will cover while driving at the same average consumption. While using 240 Wh/mile, I can no longer get the OVER 310 miles that I once did. In fact I've lost over 10% of range. I have no idea what my battery capacity really is, because nobody will tell me. Tesla sent me a chart that compares my battery capacity (how do they get that info?) to others. But it still doesn't show my capacity or what they consider to be normal now. And honestly, if every other owner has lost over 10% in a year of carefully tending to battery health, I'm not happy about just being "average" either.
Today I can get right around 50 miles for each 20% of SOC that I consume. I used to get between 60 and 65 miles for each 20%... driving the same places, in the same weather, in the same manner. I've now had the car for just over a year, so I understand the seasonal impacts (never mind that this is my 5th EV over 20 years). Again my average consumption is well under 250 wh/mile. Stats shows me down to about 280 miles of range while my real-world testing shows me closer to 250 miles. Either way you slice it, I've lost a significant chunk of range in a short period. I don't have the big gaps in the chart that some others have seen. Mine just happily drops consistently. The recent big drop from 290-280 is likely a result of it finally getting cold here.
I have local friends and neighbors with the same car... and the same age. And so far every one of them has shown no more than a 1% loss of range.... about what I expected.
Before about 7,000 miles (six months ago) I was happily bouncing along at about 308 average reported range, and was thrilled to see the battery performing as expected. And I could confidently get ~300 miles out of a single charge. But not today!