General Motors Renaissance building in Detroit. Source: General Motors.

A recall here, a recall there, recalls everywhere. That about describes the first five months of General Motors' (GM -0.04%) 2014. The automaker's count of individual recalls through May 31 has reached 36, covering roughly 15.8 million vehicles globally -- a staggering amount.

Put another way, the 13.8 million vehicles recalled just in the U.S. through May puts GM on pace to beat the industry one-year record for recalls -- 30.8 million vehicles in 2004. Surely all the recalls and negative publicity would put a dent in GM's sales, right?

Apparently not, if May's sales are any indication of the future.

General Motors drives higher
General Motors on Tuesday reported it delivered more than 284,000 vehicles in the U.S. last month, a 13% increase from May 2013.

"The momentum we generated in April carried into May, with all four brands performing well in a growing economy and 17 vehicle lines posting double-digit retail sales increases or better," said Kurt McNeil, U.S. vice president of sales operations, in a press release.

The driving force behind the sales increase was General Motors' Chevrolet brand, which posted a 14% gain over last May's sales. Chevrolet accounted for 205,010 of the company's overall 284,694 sales during May -- nearly 75%.

Sales of the Chevrolet Impala continue to move higher. Source: General Motors.

Chevrolet's uptick in sales was aided by an 8% increase in the company's best-selling vehicle, its full-size Silverado pickup. The strong Chevrolet brand performance was also driven by the Camaro, Cruze, Impala, and Traverse, which respectively posted sales gains of 30%, 40%, 23%, and 23%, compared to last year.

Each of those vehicle models topped 10,000 units sold in May; that makes them more significant to overall sales than the Corvette, which was up an astounding 267% compared to last May, but still only sold 3,328 units.

It's a bit surprising that the blitz of recall-related negative publicity this year has had little to no effect on GM's sales. One reason could be that the average consumer doesn't recognize which brands are under General Motors' umbrella. For instance, some car buyers may announce that they won't buy a GM vehicle, only to turn around and purchase a Buick or Cadillac without realizing they now own the exact General Motors product they vowed to avoid.

It's also possible car buyers are giving America's largest automaker the benefit of the doubt that these recalls were related to mismanagement and poor quality that plagued the company years ago, and aren't indicative of the company's current products.

What investors should keep in mind
Still, there is a bit more for investors to consider about last month's 13% sales gain.

Part of the company's surge in sales was due to ballooning fleet sales. General Motors' retail sales in May -- those to individual buyers -- were up only 10%, while sales to fleets were up a whopping 21%. For comparison, Ford's (F 0.08%) retail sales were up 6% last month, doubling its overall 3% sales gain. Ford's figures emphasize that sales gains at the Blue Oval were driven by retail, not fleet, consumers -- albeit at a slower overall pace than GM. 

Fleet sales are typically viewed as less desirable and less profitable sales compared to retail, though there are exceptions. More importantly is what GM noted in its press release that investors can expect a reduced June fleet sales result when reported next month. Just as the 21% surge in fleet sales last month helped buoy its 10% retail gain to an overall 13% increase in May sales, investors can likely expect the opposite to happen with June's sales results. Put simply, May pulled in a chunk of June's sales. 

GM CEO Mary Barra will hold a press conference regarding the ignition switch recall today, June 5. Source: General Motors.

Another thing for General Motors investors to watch is today's press conference regarding an update to the ignition switch recall. Early in the morning GM CEO Mary Barra will conduct a "Global Town Hall Meeting" with employees, which will be followed by a conference call for analysts and media. At the time of this writing GM CEO Mary Barra has announced that 15 employees were dismissed in regard to the company's internal probe and investigation, but the report has yet to be released in full to the public. You can find the most recent details at the time of this writing here. 

Massive vehicle recalls haven't slowed General Motors' sales yet this year, but the dust kicked up by those 13.8 million recalled vehicles in the U.S. has yet to settle. Investors would be wise to watch sales over the next quarter for signs of any negative effect.