The original paper is from the 1950s and this has been studied a lot since then.

From doing a lit review on working memory capacity, it seems that our capacity is highly dependent on the context of the task/information and the individual's expertise/skills. One particular replication study I remember was not able to replicate the results. I tried applying it to more complex tasks (e.g., coding) and it did not work at all.

I recommend Radvansky's book "Human Memory" if you want to learn more.