"filter and pass through" non YYYY-MM-DD dates when date shifting

[g-pechorin]

Is this the right issue type?

• Yes, I'm planning work for this project team.

Summary

There are now things which aren't dates in the spreadsheets. "Unknown" or "NA" or even just a year like "1983" are a problem for the current implementation;

• Text like "Unknown" should be passed through
• Years are currently treated as if they're Jan 1st and shifted as such. This leaks the date shifting offset for a given participant.

this is related to #2

Acceptance Criteria

The current approach is to manually edit the shifted Excel document after shifting it. A better approach would be to copy appropriate values and halt execution when unexpected data is encountered.

• shifting halts when MM/DD/YYYY values are encountered
• shifting accepts YYYY-MM-DD values
• Documentation strings updated

Confirm creation

• Ready to create this feature?