Yes, Larian would have to give the updates to digital distributors for them to package into a patch specific to their distribution of the game. Presumably they are working with all the distributors for the upcoming patch, so one from Gamesplanet shouldn't be delayed much, if at all, from the official release. Any additional patches in the short to mid term should be fine, as well. You could email Gamesplanet to see if they have a policy on patching support, or do things game by game (ie patch as long as the game is still selling).
Eventually certain distributors may stop making updates, but I don't know if digital distributors are any more or less likely to do so than traditional distributors. For example, the last official Australian patch for Beyond Divinity was 1.45, but the UK / North American versions got two patches after that (the last just to remove the copy protection). A registry edit will allow the 1.49 English patch to be installed on the Australian game version, though. I think the length of support from publishers for other language localizations varied. The digital distribution for Beyond Divinity started off with all the updates included, so didn't need any patches.
There should be a manual for the digital download version. Maybe nobody with that version saw the request for an upload, or they couldn't be bothered? It is possible the manual gets watermarked with your name or account number, or something, before you download it...
I don't know if anyone has tried moving saves between different versions, or if the upcoming patch would improve compatibility (since the games would be brought to the same version number).
Welcome to the forum.
