What I mean is that whenever ACF saves a value for the first time on a post two fields is created in wp_postmeta. Both field_name and _field_name where field_name contains the actual value and _field_name contains the fields internal key created by ACF.
So if field_name exists in wp_postmeta then _field_name should also exist. The exemption from this is if you create the field_name key/value pair yourself using update_post_meta (for example). Then _field_name wont exist until the post has been “updated” from wp-admin.
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