The ISO date regex copied from papaparse is a bit strict. For example the airbnb sample test data we often use has dates like:

2015-01-04 00:00:00

I've also seen:

2015-01-04

We can just make the relevant parts optional as both of those can safely be passed to new Date().

There are unit tests for this detection and we can just copy/paste and make some more. There's also test/csv/types/date.csv where we can add some examples. Some expected results may or may not have to be updated to match.

You can just focus the relevant files (.only on a describe somewhere) and run:

DEBUG=import npx mocha --bail src/import

for fast test turnaround.