In this article: 6 Rules of Thumb for MongoDB Schema Design: Part 3 | MongoDB Blog
2^8 (1024) should be replaced by 2^8 (256) and 3000 should be replaced by 750 (or any number lte to 768).
In addition, in the second and third article there are sentences like this:
Also note that if you denormalize a field, you lose the ability to perform atomic and isolated updates on that field
This is not fully correct because you can perform atomic operations in these cases by using transactions. (there is no mention of transactions in any of the 3 articles).