iCloud Mail Import Finished - missing many folders and emails

I am migrating my outlook.com email into iCloud.com. outlook.com has thousands of folders and hundreds of thousands of emails ... altogether, roughly 35gb of content/data over the past 45 years.

I'm using the MAIL IMPORT feature on iCloud.com ... the mail import feature started 5 days ago ... and it says it finished yesterday. I see no "exceptions/problems" list produced by the import history.

As I review the folders and emails on iCloud.com, I see that there are at least 100 folders and several thousand emails that didn't import.

How can I confirm/validate this process completed without exceptions/errors? is there something backend on apples servers that they can see/view to give me more direction as to what failed?

I guess where I'm going with this ... is if there's no exception produced, yet i verified not everything was ported, then how can that import process be trusted?