So, looking at geonames, I am finding that there are a significant number of blindspots regarding zipcode mappings. Many countries are missing. Some countries have abbreviated data (prefixes in zipcodes only are listed in Canada for 'copyright reasons').
So my current approach is to create a routine in the software (an open source program called LedgerSMB) which will let users export a list of country/state or province/city/mail_code mappings to a CSV file that can then be emailed back to us for processing. No identifiable information would be included and the results would be merged before distributing. My current checklist is:
An agreement with the customer that this will be going into a very permissively licensed package in exchange for validation feedback on their data.
We'd offer attribution in an appropriate form (but no downstream guarantees).
Data would be run through automated checks, and normalized prior to merging.
Is there anything major I am missing? Anything we need to think about before approaching users (many being business users who are not entirely technical) about this?