Would custom import ever fail/re-order if fields are missing

I'm creating an update to a system which has several older versions, they are runtimes, each user backs up their data (into a special fp7 file) using an inbuilt script which saves various system settings in various fields, as well as other tables for their data. Everything is locked down, runtime kiosk.

When they receive a new version they run a resoration procedure, which is a special import bringing in all their settings and data from the previous version's backup file: this could be v1 to v5, v2 to v5 etc. depending on their upgrade path.

As the system has grown, new settings and features are of course added, and in newer versions I've added these to the backup, in this new version there are many new settings and defaults which will get backed up.

Providing I always use a custom import order (not matching names) in the restoration script, if fields aren't found (e.g. when v2 is importing a v1 backup) presumably they'll just get ignored... Would there be any circumstances where the import would fail or the custom import order be changed if fields are missing?

I've done various sets of testing and can't trip it up, but we are talking a large group of installed users and if there is any danger of error, I'd rather have separate import scripts for each of the new settings/feature sets.

Thanks all.

(11v03 advanced Win 7 pro)