704 type marker back data

[Jday7879]

Pull Request Title

Summary

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Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe):

Checklists

This pull request meets the following requirements:

Creator Checklist

• Installable with all dependencies recorded
• Runs without error
• Follows PEP8 and project-specific conventions
• Appropriate use of comments, for example, no descriptive comments
• Functions documented using Numpy style docstrings
• Assumptions and decisions log considered and updated if appropriate
• Unit tests have been updated to cover essential functionality for a reasonable range of inputs and conditions
• Other forms of testing such as end-to-end and user-interface testing have been considered and updated as required

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Reviewer Checklist

• Test suite passes (locally as a minimum)
• Peer reviewed with review recorded

Additional Information

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[Jday7879]

@robertswh this code now passes unit test data. It involved removing and the back data and re applying a couple of times. It might be possible to do this alternate ways, but this currently works for back data.

[robertswh]

@Jday7879 very nice. I think that's how I imagined it would work. I think this works as a bug fix and will require a more substantial refactor to simplify the code.

[lhubbardONS]

Code all looks good, happy to approve changes