PM, RJR, and Lorillard all have there own customer date codes and the post above was correct about RJR's as it is the easiest. I don't know lorillards as I like newports but they are a little too strong for my blood to smoke all the time.
The other makers which are considered Value or Discount brands do not manufacture the same brands daily and instead focus on one brand a month (with the exception of Star Scientific). They will always have codes on the bottom but instead of being birth codes they are lot codes and this is the way they want it to be intentionally to throw off consumers from knowing the product they are buying is stale. Let's face it, we have all tried a value or discount brand and we can all pretty much say we have had a stale pack at least once. I guess it is cheaper for them to lose a customer than to refine stale tobacco into recon. I have toured discount and value factories before and I must say most of them produce a premium cigarette taste. It is the fact they sit and sit with low sales that pushes stale products out the door. Most value brands will tell you they have the same swap out/rotation policy as the bigger makers but since they market to mom and pop gas stations I think it boils down to being lazy on the part of gas stations for not doing their job correctly.
Glad this could help
.