I am a lousy synctactician but I don’t think the ’s in Scandinavian is a gentive case marker anymore. Why,? because it is attached to phrases not words. We don’t say **(Erik)s den (röde)s skägg” but (Erik den röde)s skägg.

And worse (cooler?) things: killen vi pratade om igårs mobilnummer ('the guy we talked about yesterday's phone number')

That's true in English too! But the fact that Swedish has the same behaviour and survives fine spelling it without the apostrophe only reinforces the original point.