@JohnathanHasthorpe, I also need functionality for members of the public to download records to the Inbox and be able to update them. Similar to @ChristopherMatechik, I run beach-nesting bird surveys for endangered species, which are conducted by members of the public. Each nest has its own record which has a repeat in it for daily observations to be added.
The form records the nest location, ID, and summary of previous observations as part of the parent data, so when the record is opened from the Inbox, the volunteer surveyor can see the "nest history" and can then add a repeat record for their own observation.
Different surveyors will monitor nests from day-to-day, so they cannot simply use the "Sent" box to "edit and resend" surveys, because this is only possible for surveys submitted from the same device, and also doesn't prevent surveyors from editing previously entered daily observations in the repeat section.
Keeping a single nest record for each nest avoids duplication or complication of records and allows users to view the nest history, instead of submitting separate records for every nest-day observation and doing loads of data cleaning and collating in post-processing. It also risks erroneous observations and incomplete data if surveyors cannot see what nest status details were entered during previous visits.