Not so fast! :-)
While newer version of Corel Draw can open older files, they only go back few versions. Not sure if the latest version of Corel will be able to open Core 8 files. You might need to go through an intermediate step of opening the V8 file in slightly newer version (like V12 or X3), and saving it in that version's format. Then you'll be able to open it in the latest version of Corel. Maybe someone who knows more can chime in here.
As far as not being able to go the other way, it's perfectly normal. New versions of software introduce new features and functionalities which were not available in other versions. Then the file format changes too. The older software simply does not understand the new format or has the new features. But Corel usually gives you options to save the file in older format). At least it does in the versions I use (10 and 12). So, the compatibility can be maintained for few versions back.
The Wikipedia article on CorelDRAW claims that files back to version 7 can be read. I don't know where a definitive specification might be found.
For what it's worth, I just dug up a version 7 .CDR and opened it in CorelDRAW 2018.
You are correct that, if one has assets that are far enough back in version, one may have to go through some "intermediate" version of CorelDRAW in order to get them into a recent version.