What does the input normally look like? Is it one address per line? A paragraph of text?
One issue is the word separators in FileMaker. Take this for example:
What do you think this evaluates to? (hint: it's 3). FileMaker treats this as 3 separate words.
Here is the link to the list of word separators in FileMaker:
This is where native RegEx would really come in handy...