Yes.
Here is one highly publicized example in the recent news, for the clothing store Justice:
Ohio law says stores can only advertise a "sale price" on items if they were sold at a higher, regular price for a run of at least 28 days in the previous 90 days.
Justice sales claimed shoppers would get "40 percent off." The Judge ruled that items were sold at a higher price so fleetingly the 40 percent off price tag was in fact the regular price. They had to give refunds to everyone, basically that the price they paid was regular price, and now refund them 40% on top of that.
I remember walking by the store everyday at the Mall. The "40 percent off entire store" signs where basically permanent signage in the store, all year round.
So, in the case of Harbor Freight (at least in Ohio), as long as during the previous 90 days, it was only on sale 62 days or less, and retail price 28 days or more. Then perfectly legal to call it "on sale".