Within each group folder, you will see duplicates with (1), (2) and such appearing after the name. This is because a driver may exist under both System and Net for instance. The NIC driver is commonly put in with the system drivers besides the network drivers folder, thereby causing it to appear twice.
To trim the driver list down, sort the Name field. When you find your first duplicated driver, look at the dates on the original and the dupe. If they do not match, then select the oldest ones to delete, leaving just one. Under the actions list, click Delete under the driver name, NOT under the folder name. If you click delete under the folder, the entire folder will be deleted. I have done that and could have kicked myself afterwards, so pay close attention. Once you click delete, do NOT select the Completely delete these items, even if there are copies in other folders. (Force)! If you select this, it will delete that driver across all models and types. I did this and then found out when building other model machines, they were missing those drivers. I had to go back and re-import the drivers for every model. When you leave it unchecked, it only deletes the pointer to the driver and not the actual driver.
Next, you will see duplicate drivers, except with different versions. You will most definitely want to clean up this list so that only the latest driver is there. For instance, I had one model that had 6 versions of NVIDIA Display NVDW.INF in the list. I deleted all, except for the latest one. I also made sure I only deleted it from the list and not completely from the folder.
This not only cleans up the number of drivers copied down during the build, but it also ensures the latest driver gets installed too, as I do see on occasion that the older driver got installed.
NOTE: Before you do any of this, make sure you have the original drivers that you imported into MDT in a windows folder, as if you make a mistake and need to re-import them.