If I understand it correctly, you installed a fresh OJS 2.4.8-1 and then tried to somehow import the data there? -- This is not a good solution, because one cannot migrate everything this way (e.g. statistics and workflow processes, decisions and communications).
Considering statistics migration:
In the upgrade script (s.https://github.com/pkp/ojs/blob/ojs-stable-2_4_8/dbscripts/xml/upgrade.xml), these scripts and functions are run before the DB changes for your migration, from 2.4.2 to 2.4.8-1:
then the DB is updated:
and then these scripts are run after the DB changes:
Thus you would somehow have to rewrite those migration scripts to work on your both DBs -- to migrate data from one DB into another.
And, as I said above, even then you could be missing some other data... Thus I would recommend to try to fix the upgrade solution/version...