Trying to identify Dad's lost watch.

[ten6610]

Hi to all,
Unfortunately I have no reference numbers or paperwork for the watch, and photos and 1990's VHS film of it are either not close-up enough, or out of focus.
I understand Dad purchased the watch new, in Switzerland, around 1973. It was an Oyster Perpetual Date Just, Chronometer rated, with a Champagne, "stick" dial, and fluted bezel.
Due to the poor quality of the visual record, I am having difficulty determining the carat value of the gold used in it's case, versus that used in it's bezel, as it is apparent, at least to my eye, that both are gold, but each has a distinctly different hue, or color. To some this difference makes them feel the watch case is stainless steel, but I don't agree.
I am trying to establish a replacement value for insurance purposes, and the watch-maker I am working with has just told me he recalls Rolex producing this watch in the early 70's, and offering a lower carat case than the standard, matching, 18 K case and fluted bezel.
Is it possible that Dad's watch could have had a 18 K, 16 K, or 14 K fluted bezel, mounted on a case that was less than 18 K? I can provide images, but they aren't the best. Any help is appreciated. Thanks.