If you're a recent Chevrolet Volt buyer and noticed you've been getting a few more miles out of your all-electric range than you expected, you might've gotten next year's version of the extended-range plug-in.

This month, General Motors started delivering a few 2013 model year Volts to Chevrolet dealers across the country, though the automaker hasn't publicized the changeover, both Green Car Reports and Hybrid Cars report. Green Car Reports says 2013 Volt availability is "spotty," while Hybrid Cars says GM has "sprinkled in" a few Volts. Production of the 2013 Volt started in early July.

GM said last month that the 2013 Volt boosted its all-electric range by three miles – to 38 – compared to the 2012 version while increasing its miles-per-gallon-equivalent rating by four to 98 MPGe. GM also said the Volt's battery capacity increased to 16.5 kilowatt hours from an even 16.

2013 version or not, Volt sales are on the upswing. GM sold 8,817 of them through the first six months of the year, more than three times the number from this point in 2011.