Original dial --> Same dial as it came out of factory, without any later man-made modification. Of course it may be patined, damaged, dirty, etc...
Redial --> The original dial after being modified by man (painted, "refurbished", "refinished", etc)
Service dial --> A new (at time of servicing), originally Omega dial replacing the original one. Not necessarily identical to original dial.
That's how I understand it, not necessarily how it is.
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