What i normally do is to import all the applied entries first. And when i do that i use the apply to oldest method.
Once all appliced entries are imported i switch to apply manually when i import entries that are open at the time of migration.
The apply to oldest will usually not match 100% the application that was done in the old system but at least only open entries from the old system will be open in Business Central.
Another strategy is to simply skip all old entries and just migrate the open entries.