If you import xml made in Snap 8.2.3 into Snap 8.0.0, then some conditions turn into not defined labels. We need a warning about the reason for such an error!
Not (m)any programming languages in the world are backwards compatible 
No warning required
If you're importing a project from a future version of snap, you should expect that things will break. There's not really a need for a warning, since it should just be common sense.
An example is, you cannot import a scratch 3 project into scratch 2, even though scratch 3 has virtually the same blocks as scratch 2, the difference is actually just the file format.
this isnt a bug try to put a switch cartridge in a nes
xml files use text code to program for each block ex.
But in different versions of snap the XML file is formatted differently which the older versions cant read as you cant update the old update (I hope that explains it better)
here's a XML tree of snap 7 and snap 8.2 for comparison
why are you talking to me and not op?
Most false information I’ve ever heard in my entire life
why is everyone replying to me
Because you are saying something that’s just straight up not true
admins close this topic we have a solution and the posts are getting too off-topic
oh sorry about that i meant to tell op
ohhhh the sd card thing you know what im just gonna delete it
There are really three situations that might be happening, so it's hard for us to provide a perfect error message. If you deliberately run a new project in an old copy of Snap!, then yeah, we can tell you not to do that, but as everyone else is saying, you shouldn't really be surprised. The second situation is that you write a project in Snap!, then import it into a Snap! fork such as Turtlestitch, which doesn't yet include the latest Snap!. That's not your fault, but they really have to give you the error message; we're not in charge of their code. But the third situation, which really could use a better message, is that you think you're running the latest Snap!, but because of browser caching errors, you really have part of the new version and part of the old version. I guess we could check the dates of all the loaded source files to detect that. We do post to this forum, the BJC forum, etc., when we become aware that this is happening. To be clear, the browser is supposed to make sure it doesn't happen; it's not something we did wrong. But we could still suggest a hard refresh.