The letters actually refer to the connector shell size and are really independing of the number of pins. For example, a DB shell could have fewer than 25 pins. Some have two or even three heavy pins (one for power, 2 for return) and some signal pins. The reason the the 9-pin is designated DE is because it was developed after A, B, C, and D, sizes.
What are the engineering and design challenges in creating successful IoT devices? These devices are usually small, resource-constrained electronics designed to sense, collect, send, and/or interpret data. Some of the devices need to be smart enough to act upon data in real time, 24/7. Specifically the guests will discuss sensors, security, and lessons from IoT deployments.