Unless you can show such a policy, it is reasonable to assume it does not exist. I surely have no way to prove otherwise short of finding complete list of all policies. A good indication is that neither of us heard about it so far.

If we have no evidence, it is not "reasonable to assume" anything.

Meanwhile, I'm merely saying that it wouldn't surprise me if such a policy exists, whether formally or informally. The distinct lack of any product on Walmart shelves which has a below-RRP price printed on its packaging is strong circumstantial evidence at the very least.

It is reasonable due to the Occam Razor.

The fact that you mentioned is an extremely weak evidence in the light of very thin margins Walmart has (under 3%), which is more than 10 times less than the old store tax, with probably even smaller incentive to combat.