The documentation for the index API says this about the external_gte version type:
NOTE: The external_gte & force version types are meant for special use cases and should be used with care. If used incorrectly, they can result in loss of data.
What is the reason that the external_gte version types needs to be used with care? What type of care needs to be used? How can the external_gte version type result in data loss?
Is the issue that a failure of the external system to properly update the version number on a change to the data could result in incorrect data being indexed? If so, I believe that issue can be avoided by making sure the external system behaves correctly. Or, is there a more fundamental issue that can result from using external_gte?