1pux export data will be wrong or old (and uncomplete)

It comes to my mind you really may have old data in your vaults, for example you might have used 1Password 7 with a local vault and copied data from the cloud to your local vault, for example for backup purposes, and the vault data become stale because you actually edited the cloud data only.
With the upgrade to version 8, the client offered to upload any local vault to the cloud, and you accidentally uploaded your stale/old vault, and now you're seeing this in the export.

It also may be you used different accounts in the past for trial, and you exported some trial account with old testing data instead of the accout where you manage your current data. After all it's possible to be logged in with multiple 1Password accounts, so you might have chosen the wrong one to export.

Or you're exporting with an app that has broken cloud sync and you didn't realize this.