Thank you for your answer. I think until now there was nobody else, who had an explanation for that phenomen that Archduke Carl Ludwig is/was the only son of the emperor, who is buried (or will be buried) in Vienna in the Kaisergruft. There are now only some days left.
But yes, that sounds logical. Is the birth under the reign of Karl I. the offcial reason or is this speculated? You will know it. It seems, as it sounds, this is the really the official arguement. I would not have expected it, but to be honest, I also did not think about such a reason.
You're lucky that you have the possibility to attend the funeral. Even some family members don't have the possibility, as I know.
Any infos, how the funeral proceeds would be appreciated. Maybe you can give some infos here, after you took part in the event.
That would be nice. Thank you, Eurohistory!