If the resource fork isn't roasted by a non-Mac OS, then the type/creator info could be lost as well. Type and creator can be modified in ResEdit or CreatorChanger, or the like.
System 6 doesn't really support hot-launching associated applications for certain documents. System 7.5 is a bit better for that but all throughout the Classic OS range it's a bit of a sore point. For instance you might download a driver compressed into a .sit file into 9.2.2, then try to open it like you would normally do and it kicks back a dialog saying it doesn't know what application is associated with that file type when Stuffit Expander is on the system. Part of the reason for this is Macintosh Easy Open more or less has to be manually configured for odd file types for it to do this.
It really wasn't until OS X that this became more intelligent. Although Windows can do the same exact thing, if it doesn't know to associate .dwg with AutoCAD then it'll pop the dialogue asking which application to open it with.
SE/30 Cap Replacement http://tinyurl.com/7r7jjor
Classic Mac Networking http://applefool.com/se30/
"Linux assumes you know exactly what you are doing." -oboedad55, ubuntuforums.org