Certified pre-owned sales continue to climb and hit records. And used-car inventories are getting younger at franchised dealerships, with 58 percent of their used-car inventory in the second quarter at 3 years old or newer, according to Edmunds.com.

In its Q2 2016 Used Vehicle Market Report, Edmunds said 22.6 percent of franchised dealers’ used-car sales in the second quarter were CPO units. This was on par with Q2 of 2015, when 22.9 percent of their used sales were certified.

So that begs this question: If CPO sales are at record highs and franchised used-car inventory is skewing younger, why has CPO share of franchised dealers' used-car sales only remained flat?  And will that share increase as the year goes on?

The team at Edmunds looked into those questions and shared some insight, pointing out that certified vehicles tend to take longer to sell because of their higher prices.

“So, yes, we are getting many lease returns (and expect more in the future) but the time horizon in which they sell is longer and more volatile,” a company spokesperson said in an email.

“Cheap used cars sell quick and easy. Expensive used cars, not so much. The relationship between franchise used and CPO may not always look the same quarter to quarter,” the spokesperson said.

However, you can expect increases in the CPO share of franchised used down the road.

It’s a “two-fold effect,” according to Edmunds. Not only are there more cars coming off lease, there has been a slowdown in the percent of new-car buyers who bring a trade-in through the front door.

In the second quarter, 45 percent of new-car sales had a trade-in, according to Edmunds. That is down from 48 percent a year ago and 51 percent as recently as Q2 2012.