Gas Gauge bars vs. computed MPG

Hi folks. First off, apologies for another post on the gas-gauge pips situation; I did spend some time reading through old PC forum posts before this, but couldn't readily find an answer.

2007 Prius purchased new, now 97,000 miles.
My mileage (as displayed on the center console) seems to be pretty constant over the last 15 years. I reset the console stats on every fill-up. I see 49-53 MPG (console calculated MPG) in summer driving and I see 43-47 MPG in winter driving.
By that reckoning, I've grown accustomed to "a summer tank is good for 375-400 miles" and, "a winter tank is good for 325-350" before I start looking to fill up... (Generally thinking ~8 gallons between fill-ups.) In fact, this often corresponded to fill-ups in the 7-8 gallons range. A 9 gallon was pretty rare for me, and I don't think I ever hit a 10 gallon fill-up. I generally don't wait for blinking 1-pip on the gas gauge; I will usually fill up at 2 bars. Now (~last 2 years?) the gas gauge runs down to 1 bar much more quickly, usually before 280 miles travelled. Well before the computed-MPG against tank-miles-driven would suggest I should be running low -- assuming an 11.9 gallon tank.

Example from this week:
Filled up fresh for a 415-mile-long interstate road trip. (oops - I put more gas in, topping up after the pump-shut-off... Something I've done on probably 50% of my fill-ups over the last 15 years... sigh; missed the memo not to do this practice!)
After 298 miles driven, the gas gauge started blinking 1 pip. I recall reading that the blinking is designed to start when approx. 2-3 gallons remain? So blinking would imply I used up approx. 9 gallons; which would yield here, a trip-MPG of just 33. But the computed MPG was showing 47.1 for the trip. Based on that computed trip MPG I should have only used ~6.3 gallons; a far cry from nearly emptying the tank to trigger the blinking. But out of caution I stopped for a fill-up; and took in ~6.5 gallons til the pump clicked off. So that would seem to support the console calculated MPG is pretty accurate for determining how many gallons were used for the miles driven...

My question - is there a way to tell if my tank is in fact still able to hold ~11.9 gallons at a fill-up? And if it is still holding a proper, full tank, then in this trip's example, it seems I could have travelled say, 423 total miles (47.1 x 9 gallons) before looking to fill up?
IF that were true -- I gather the blinking pip would simply have continued blinking at me for another 125 miles of travel...?
I guess I'm not sure -- is the blinking 1 pip a legit indicator of true remaining gas available -- implying my tank no longer holds close to the original 11.9 gallons, and the systems are correctly telling me I will in fact soon run out of gas and the car will stop...
Or, has the gas gauge fallen out of synch / no longer reliably indicates the amount of gas remaining -- but the computed MPG figure still serves as a reliable way to determine gas consumed so far (and thus forecast the remaining travel miles available) based conservatively on aiming for 9 gallons burned between fill-ups?

I mean, I really want a 2023 Prius Prime, but I'm not ready to buy a new one just yet Thanks in advance for your input...!

 

Such a helpful reply... thanks for taking the time!

 

Thanks, done and done!