The HP Museum site (HP-35 (hpmuseum.org)) mentions a first version prototype of the HP-35 with a whitish case and no front label (under the keys). It seems the same case was used for a HP-80 prototype which I own.
The calculator works well and is a full fledged HP-80 as far as I can tell. I am not sure of the fabrication date of the calculator but indeed, the case seems to be identical with the first HP-35 prototype. It is conceivable that one could read the integrated circuits labels to assess the date, but the back label is pristine and I did not want to disturb it by taking apart the calculator.
In the beginning I thought the case was “borrowed” from a HP-70; however this is not the case. The last two images show a HP-70 along this calculator, there is a clear difference.
An interesting find.
