Maybe. Depends on your driving style and conditions. I likewise have a low miles '08 that I bought 2 years ago. and I've only seen 3 tanks as low as 42.3. All 3 were 75mph banzai road trips in mountainous country. Day-to-day driving nets me +/-52mpg in non-a/c season and +/-49mpg with a/c cranking.
45-46mpg was what I used to get when my Prius was new in 2008 & Never more than that!!! 42.3MPG for the last 2 years=Is the new Norm.
My '08 did about as well. I could squeeze a couple more mpg out of properly maintained tire pressures 2-3 psi above Toyota recommended. When my 12V went bad it took the mileage way down. Winter driving took a toll also. I fiddled around with carefully cleaning the throttle body and MAF for a couple more mpg. Your number appears to be lifetime. I used the vehicle estimate and reset one of the trip odometers for each gas tank fill. Also didn't document, just kept a "running" figure. If it was better than 40 mpg, it was good.
