Date ranges (e.g., 2014/2019) are incorrectly parsed as single year in metadata

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datasets version: 18.15.0
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Describe the bug

Date ranges are not correctly downloaded with the datasets CLI. Sequences with collection date ranges in the format YYYY/YYYY (e.g., 2014/2019), which is a valid ENA format, are truncated to only the end year in the downloaded metadata.

For example, sequence MW179421.1 was collected between 2014 and 2019 (shown as 2014/2019 on GenBank), but datasets reports only year=2019 in the metadata file.

This affects all NCBI entries with this date format.

Impact: This is problematic for temporal analyses and phylodynamic inference, as the date uncertainty/range is lost, potentially biasing tip date calibrations and evolutionary rate estimates.

Indicate what operating system you're using

Linux (WSL)

To Reproduce

Steps to reproduce the behavior:

1. Run:

   datasets download virus genome taxon "39054" --no-progressbar --filename data/ncbi_dataset.zip
   

2. Unzip and open data/ncbi_dataset/data/data_report.jsonl
3. Search for accession MW179421.1 and check collectionDate

Actual output:

"isolate": {
  "collectionDate": "2019",
  "name": "ZY2017-12-EV71"
}

Expected behavior

The date range should be preserved, either as:

• Original format: "collectionDate": "2014/2019"
• Structured fields: "collectionDateStart": "2014", "collectionDateEnd": "2019"

Currently, only the end year (2019) is retained, losing the 5-year uncertainty window.

Note: This issue appears specific to the / format for date ranges. Other range formats have not been tested.

Run the reported datasets download virus genome taxon command, then inspect data/ncbi_dataset/data/data_report.jsonl for accession MW179421.1. Compare collectionDate with the ENA value 2014/2019; the work is done when the downloaded metadata preserves the range, either in its original form or as explicit start and end fields.