How testing Mach-O files to see if they’re Universal Binaries gets complicated – and probably isn’t as reliable before macOS 10.14.
How can you tell whether an app on your Mac is a Universal App, or only support Intel processors?
You’re checking through old files. How can you tell which file type they are when you don’t recognise the extension, or they don’t even have that to help?
Telling what a file is – whether plain text, Unicode UTF-8, 32-bit code, and so on – can be hard. Just use a little magic, free in the command tool ‘file’. Includes Swift code to access magic numbers.