(FORTUNE Magazine) – A necessary evil in good times, inventory can turn into an outright demon when it piles up in a recession and keeps recovery at bay. That didn't happen last year, as responses from 175 executives in FORTUNE's exclusive quarterly survey of inventory policies reveal. But fresh government data raise perplexing questions about just how business is managing its inventory these days. Before the recession, the executives let concerns about short supplies or rising prices temper their resolve to keep inventories tight. In the past year and a half, though, a fairly consistent two-thirds have said they would rather risk coming up short than overbuying. Some got stuck anyway. In every recent survey of ours, nearly 30% have reported that weaker-than-expected sales left them with more stock than they had planned for just three months earlier.

Nonetheless, excesses never built to the point of threatening recovery. Businesses have typically kept inventory-to-sales ratios in a narrow range, at about the levels of 1989 and early 1990. They tell FORTUNE they would like to pull the ratio down by more than two percentage points. Still, they plan to add a bit during the coming year, saying they expect sales to grow more. Now for the mystery. After more than a decade of struggling to shrink stockpiles, business had succeeded in lowering inventory-to-sales ratios considerably -- or so it seemed before the Commerce Department's recent major revision of U.S. economic history. Though preliminary and incomplete, the new data show no significant progress: Overall, the ratio is about what it was a decade ago. So what happened to manufacturers' just-in-time policies and the quick- response technology adopted by retailers? Surveys such as ours make it clear that individual companies have tamed the monster -- and not just a few of them, judging by the behavior of total inventories during the recession. Without waiting for all the numbers to crunch, three possible explanations stand out. First, the growth of imports means that the least inventory isn't always the most efficient. When critical supplies come from another continent, you need to keep more on hand. Second, one company's just-in-time may mean heavier inventory for its domestic suppliers. For example, in this latest survey, makers of motor vehicle parts reported twice as much excess to FORTUNE as other companies averaged. Third, look to the explosion of retail stores during the 1980s. More shelves to stock mean more inventory in the system, even if each store keeps smaller piles of merchandise. As the revisions produce further information, a combination of these and possibly other factors will likely be confirmed as reasons for the surprise. What's clear for now is why business still wants to push inventory-to-sales ratios lower.

CHART: NOT AVAILABLE CREDIT: FORTUNE CHARTS CAPTION: Ratio of inventories to final sales of goods Change in business inventories