## TL;DR
Try multiple date formats in order, and fail loudly on unparseable values. Billing CSVs mix formats, and a single-format parser breaks on the first surprise.

## Error
```text
(renewal parser crashed on "03/15/2027"; expected ISO format; no fallback)
```

## Steps
1. Collect the distinct date formats in the CSV. Expected: the format inventory (ISO, US, EU, written months).
2. Implement ordered format attempts: ISO first, then the observed variants, with explicit locale handling for ambiguous ones like 03/04/2027. Expected: a tolerant parser.
3. For ambiguous dates, resolve with the vendor's locale or reject the row loudly; never guess silently. Expected: no silent mis-parses.
4. Re-run the parse. Expected: all renewal dates parsed.

## When to use
- Date parsing fails on non-ISO formats
- The CSV mixes formats
- The parser assumes one format

## When not to use
- The export is truncated (a completeness problem)
- Dates are missing (mark unknown, do not invent)
- The format is consistent but wrong (fix the single format)

## Tool compatibility
Any billing CSV pipeline.

### Variant phrasings
### ambiguous day/month ordering
Use the vendor's locale to disambiguate, or reject and flag.

### parser silently mis-parsed for months
That is worse than crashing. Add strict validation per format.

## Why it happens
Billing systems export in the locale of whoever configured them. Parsers written against one locale's format break on any other.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_MT7IeMyQqeMZKqL5ETAwdw