Copying over OC3.03.2 Customer Database to OC4.02.3/4.1 - some challenges to be aware of..

In trying to copy customer information over from OC3 to OC4, I have come across some additional "challenges" - raising this more to help anyone else trying this but also hopefully get some solutions :

Zones
There appears to be a disconnect between the zones in OC4 (4031) compared to OC3 (4108 zones).
For example (see attached), Denmark has 16 zones in OC3 whilst there are only 6 showing in OC4.
What's the reason for the difference? - is it just catching up with the latest geo/geo-political changes or have some been dropped by accident?
If catching up with changes, guess the only way to deal with it is to manually check each one in the error log? (it would be helpful if there was a simple spreadsheet available that showed what the new zone is for each old zone where there is a change)

Passwords
As highlighted on github by MHC, it is impossible to copy over customer's existing OC3 passwords to OC4 as Salt is not used in OC4. Appreciate that different methodology may be being used to better secure passwords, but there does need to be a way to provide backward compatability to make the change as simple as possible!

General Comment
For anyone attempting this, also bear in mind that fields like FAX are no longer included so remember to delete the column before you try to copy the data over!

Yes, I think the 'salt' field should be kept in the oc_customer DB table, for backwards compatibility for old customer records which relied on the 'salt' field. The 'salt' field can be ignored for new customer account creations which uses a newer technique for hashed passwords.

For more details, see the github issue at: https://github.com/opencart/opencart/issues/14416