Okay, I am sure that I saw at least one other 375/6 that I saw at Waterloo East did not have it's pantograph which is why I was asking the question. But if it is the case that 375/6's did not loose their pantographs, then I am very likely mistaken about the 375/6 that I believe I saw without a pantograph.
Found elsewhere:
The class 375/6 are dual voltage units, delivered complete with
pantographs, but have never used the AC equipment in anger (except
maybe for some tests, I don't know) and several have had the
pantographs removed.
Now to once again ask why was the 375/6 was installed with AC provision. It has been hinted many times that the fleet was intended to operate CTRL-DS services on High Speed 1 once completed but a technical engineer for Union Railways on another group has already posted a deep technical explanation as to why the Electrostar is inadequate for operation on HS1. It is understandable to assume that the /6s maybe were indeed intended for CTRL-DS because the quantity of sets ordered almost matches the current Hitachi fleet: x30 class 375/6 vs x29 class 395.
Other sources suggest that the AC provision was installed purely for future cascade to AC routes but why just the /6s and not the entire of the remaining later fleet of 3/7/8/9? The Electrostar is a modular product and conversion between AC and DC is a mere pre-loaded plug-'n-play transition. I have been explained that if all components are available an Electrostar can be converted from AC to DC or vice versa in just 30 minutes.
I also don't understand why the classes of 375/3/7/8/9 and 376 are numbered as AC sets in the 3xx series, technically they should be numbered in the 4xx series as 475 and 476 because they are operating on DC only - conversion to AC is merely just an option. Imagine if the 450s that currently operate on DC only being classified as 350s purley because they can, if need be, converted to AC...