Fix for that is to use whole word, this way you would not care about specific formatting
regex: something
- \b\w\b
then create examples like
intent: whatever
examples: |
- plate number is [example1](something)
- plate number is [example2](something)
- plate number is [example3](something)
and so forth…
You do not need stories to extract the entities. Even if you do not specify a pipeline, RASA default will pick something good for you.