Early indications are that May was another solid month for used-car departments at franchised dealers, including their certified pre-owned operations.

Citing data from the National Automobile Dealers Association, Cox Automotive chief economist Tom Webb said in a monthly commentary released Tuesday that franchised dealers’ retail used-car sales were up 5 percent in the first four months of the year.

That’s part of an overall retail used-car market that was up 6 percent, Webb said in the analysis accompanying the latest Manheim Used Vehicle Value Index, citing NADA. The same data indicates used sales were up 8 percent for independent dealers and 5 percent for private parties.

“Preliminary numbers and channel checks suggest sales rose again in May,” Webb said in the report. “Likewise, CPO sales, which were up 6 percent in the first four months of 2016, increased again in May, according to preliminary numbers.”

As for the most recently available final data on certified pre-owned, the CPO market in April was up more than 8 percent and approached 233,000 sales, according to Autodata Corp.

Autodata said there were 232,853 CPO sales last month, which beat year-ago figures by 8.3 percent and pushed the year-to-date tally to 879,211 sales (up 5.9 percent).

In the first quarter, CPO penetration of franchised dealer used-car sales remained essentially static from a year ago at 21.7 percent, according to Edmunds.com.

Typically, current-year CPO parallels leasing from three years prior, explained Edmunds director of industry analysis Jessica Caldwell.

And with off-lease volume being the story of the year in the used-car market, it’s a bit puzzling as to why CPO hasn’t yet taken a greater share of the franchised used market.

In due course, though, certified should pick up a bigger piece of that pie, she said.

“The inventory is there,” Caldwell said in a May phone interview. “There’s nowhere really for it to go at this point but up. So, I think that’s why it was a bit surprising.”

Edmunds anticipates that the CPO share of franchised used sales will increase as the year goes on. It may be an odd timing situation, Caldwell said, where more lease returns are hitting the market later, therefore bumping the full-year CPO penetration rate higher than what was seen in Q1.