To answer at least one of the questions:
If the v_tax_class_title is provided, then the associated tax_class_id is pulled from ZC using the EP4 function: ep_4_get_tax_title_class_id. But, the reason that an issue is being seen is that the 0 or empty quotes from the export is not converted to an integer on import. So, if wanted to try to "patch" the software instead of using an up-to-date version, could cast that and any other data expected to be an integer (ie. Those typically ending with _id). So instead of the inline
Code:
='" . $v_tax_class_id ."'
Could instead use:
Code:
='" . (int)$v_tax_class_id ."'
Though, even then the single quote wouldn't be necessary because the content to be stored is a number not a string, so would use:
Code:
=" . (int)$v_tax_class_id ."