Ah, sorry. I misread the direction of your migration.
Unfortunately, you will need to translate the value of each galley, article, and issue in either the metrics table data or in the historic access logs in order to move the metrics from the single journal install to the multijournal install. That is, if article 101 in the original site is now article 200 in the multijournal site, you would need to look at the metrics.submission_id and metrics.assoc_id (where the metrics.assoc_type is 257), and replace the old 101 value with the new 200 value.