Hi Cappy,
If you have entered post ID in post_id column then it must be referenced to WordPress post ID. By importing you can not set post ID which not exist in WordPRess posts database.
You can import as many listings you want in a batch.
> Update listing if post with post_id already exists.
< If post with post_id already exists in posts database then it will update that listing OTHERWISE it will create a new listing with new post ID.
> Ignore listing if post with post_id already exists.
< If post with post_id already exists in posts database then it will skips updating that listing OTHERWISE it will create a new listing with new post ID.
For more on import/export see: https://wpgeodirectory.com/docs/core-export/
Thanks,
Kiran