Ah, the smoking gun!
Thanks for posting that picture again. Definitely Platinum. Clearly the evidence is overwhelming. But that one sticking point remains. Is the box indeed original to that Mac? Seems highly likely ... I'm just bothered by the paucity of evidence of more Platinum 512Kes in all the years I've been looking. If only you had only bought it ... ;-)
What kills me is that since the long keyboard was a selling point, and the box was clearly new, why didn't they use the picture from the 512K/800 (as long as they were sticking with beige anyway) which would have been new in the US, certainly? perhaps they didn't want to promote the 512Ke? If they had a picture of the actual Platinum 512Ke, it would have looked for all practical purposes like the Mac Plus sitting on a shelf.
But, since this is the only KNOWN example of one, it makes me wonder if this is indeed the original packaging for the pictured Mac, and if so, was it actually sold in a retail space? Or was it for all practical purposes sold only as the Mac ED in the US, using the old model number and 512Ke box, until they discontinued it altogether, and replaced it in the US with an actual ED to further consolidate resources - if that even happened? For that matter, what kind of box did the ED ship in? Did it say ED, or was it a regular 512Ke, 512K/800 box, perhaps with a sticker? Indeed, if Apple chose not to update the image on the Platinum 512Ke boxes, why would they be any more inclined to update in Europe? And how many 512K/800 boxes have we actually seen? Not many, making a post 1987 box sighting even less likely considering the reduced numbers inevitably sold.
BTW - did you ever get the serial number for that Mac?