By Jinjoo Lee

Off-price retailers' share prices are holding up remarkably well despite a dismal last quarter, a testament to their postrecession track record. Investors should still approach them with some caution.

Both TJX and Ross Stores said they lost more than half of their sales in the quarter ending May 2 compared to a year ago. You wouldn't guess that from their share prices, which are down a fair amount from the start of year, but still basically flat from one year ago.

These two off-price retailers, alongside Burlington, need physical stores to sell. The coronavirus lockdowns meant they lost out on almost two months of business. None of them use e-commerce in any meaningful way and don't plan on starting to depend on it: TJX relies on it for 2% of its sales and Burlington even less, while Ross Stores has no online selling platform at all.

Investors seem to understand that last quarter's reality isn't permanent. Early numbers look promising. TJX began opening some of its stores earlier this month, and for the roughly 1,100 stores that did operate for at least a week, sales during that time window exceeded the previous year's. Some of that was buoyed by pent-up demand, as shoppers rushed to buy items they had been meaning to get.

Investors are also optimistic based on the off-price retailers' tendency to perform well during and after downturns. When people start to open their wallets during economic hardship, they turn to discounted places. While the S&P 500 lost more than 14% of its value from December 2007 to December 2010, TJX and Ross Stores gained 55% and 147%, respectively.

Still, off-price retailers are especially at the mercy of the virus' course because they have no e-commerce to fall back on. Other countries around the world have reopened and shut some of their businesses again when there were subsequent waves of infections.

It's also hard to ignore the possibility that some market share could have been taken by online shopping channels during the lockdown period. There are plenty of steeply discounted options online, some of which apparel brands have set up on their own.

And unlike previous downturns, the rummage-heavy, treasure hunt-like aspect of off-price shopping seems to be much less appealing in the age of the coronavirus. So far, the reopening of bricks-and-mortar stores has created more an awkward dance of caution, hardly the "retail entertainment" kind of experience TJX would like to provide its customers. Even though many states have started reopening across the U.S., foot traffic for apparel stores was down 93% as of the second week of May compared to a year ago, according to ShopperTrak.

TJX's shares trade at almost 1.8 times the previous 12 months' sales per share, above the 10-year average of 1.42, while Ross Stores sells at 2.37 times, also above its 10-year average of 1.78 times, according to FactSet. TJX's strong early sales numbers and off-price retailers' history show they will eventually have no problem with demand for cheaper choices. But that is demand that can only be realized through stores. That should give investors a bit of pause.

Write to Jinjoo Lee at jinjoo.lee@wsj.com