Agree. All my MultiMarkdown notes have a unique time stamp (e.g. 20191124211219) hidden in the metadata. It’s also a good idea to not rely on one app and to use plain text.
The time stamp idea:
The reason why Christian and I decided to use a time-based ID is this: A moment in time never repeats. If you identify a Zettel with is creation time, this time will become a truly unique ID. The timestamp is therefore a handy means to achieve uniqueness without worrying too much about anything else.