Dell Monitor Naming Convention

Hello, I have been trying to determine the naming convention of Dell monitors. After chatting/speaking with a few various representatives from different departments, no one seems to know what the alphanumeric characters in the model number mean. Here is the example I have been using: P2815Qf or written differently: P-28-15-Qf What I've learned thus far is the meaning of the first five characters... P - The monitor type, or series. This can be P (Professional), T (Touch), or U (Ultrasharp). 28 - The size, in inches, of the monitor. (this one happens to be 28") 15 - The year of the monitor's release. (they must be like cars, where you can get the '15 model in 2014...) But now comes the remaining characters... I've noticed that there are typically 2 noted on the actual hardware - "Qf" in my example above - but only one when purchasing from www.dell.com. Sometimes these are noted as the "P2815Q Series." So what do the letters after the numbers mean? In this specific case, the "Qf". But I've also seen "Hb," "Hm," "Mb," "t," "F," etcetera. I have a hunch that they deal with the resolution, refresh rate, aspect ratio, color depth, etc. They must mean something. Also, I'm not trying to find out what my example means/is capable of, I can look that up. But rather, what are all of the other possibilities? And just to complicate things... There are some that don't fit the mold above (Dell E198FPf). Perhaps that's an old style and was before Dell came up with a solid naming convention. Thanks in advance for thoughts and replys.