I am not convinced that Walmart was ever a penny stock.
It IPO'd in 1970 at $16.50. In order to be classified as a "penny stock", it would have to dip below $5 a share AND have less than $2 million in net assets.
I do not believe either one of those things ever happened, much less both of them, that would throw Walmart into the Penny Stock category, as it was listed on the NYSE 2 years later. And back then, the NYSE had much higher listing standards then they do now.
Due to all their splits since then, on a split adjusted basis, their NYSE listing price was in the pennies. But that again is the usual mistake of people who can't read a split-adjusted price chart.
The stock never ever traded in pennies.