There was no dimensional c-scar on the original helmet.
It does not appear on original castings from the baker mold, or the uk mold that created the ESB/ROTJ helmets.
This detail was had been debated for years.
The TM and SL camps cannot even agree on whether or not the c-scar was a scratch, or a raised line, or a paint flake. (the answer is none of those things)
There are two camps that are pushing for the c-scar to be dimensional.
The TM camp and the SL camp.
The TM
The original TM casting was an ESB style casting and had already been painted up by the previous owner.
The paint was stripped down and the helmet was molded.
A casting was cleaned up and modified by JRX (Jesper)/Trap Joe (Joerg) and that master was molded. (not sure which of the two did what step).
This modifications and clean up to this master included a lot of things.
The tusk tubes were re-sculpted on, the c-scar area was added and general clean up was performed over the entire surface of the helmet.
Castings were made available to a small group (all of which live at the prop den).
I do not know if the owners of these castings were even aware that the c-scar area of their castings is there because it was added in by JRX. Perhaps he never told them. JRX is a talented sculptor and has a history of modifying cast from original items to include details that he thinks they should have (when in reality they shouldn't). Check out his vader armor if you want a good example where he added tons of brush stroke texture- in the end it looked more like wood grain).
The SL
The SL was a casting acquired by Sithlord on ebay and it was determined to be a casting out of the baker mold.
This casting suffers from dome and neck flare (most likely due to a rushed casting job by a naughty ILM employee) as well as a broken left tusk tube.
Just like any other casting from the baker mold, the SL also does not have a dimensional c-scar on the cheek.
The SL was molded by Ghost Host, and castings were made available to their small group. (all of which live at the prop den).
People in the TM and SL camp were of the mind that the c-scar was a dimensional detail on the original helmet.
When they acquired castings that did not have dimensional c-scars, in an effort to make their castings appear more authentic, they added this detail in (or at least, the person doing the clean up and molding added it in).
Like I said above, it is very likely that the other people in their group was not aware that this detail had been added in, which would explain (partially) why they are defending it so vigorously.
Here are some comps of the TM showing the original TM casting once it was stripped of it's paint next to one of the cleaned up TM castings with details added/removed.
Another couple shots of the original TM without any c-scar.
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