Each model is only compatible with one Semi-structured layout, but a model is not necessarily compatible with every version of a layout.
Compatibility logic is determined by comparing fields that the model was trained on (e.g. fields in the live layout version at the time of training initiation) to fields in the live layout version, excluding table-column fields.
Compatibility with Live Model
If the model includes the fields that the active layout version also includes, then the model will be compatible. However, if a live layout version includes fields that the model was not trained on, then the model will be incompatible.
If you delete a field in the layout editor and re-add it, it will be considered a new field.
A live model will continue to work even if it's not compatible with the live layout version, however, the model will not be able to find the new fields. You will see a warning on the Model Details page of which fields the model was not trained to find.
Compatibility with Candidate Models
You will not be able to deploy a new Candidate Model when it is incompatible with the live layout version. The Deploy This Model button will be disabled and you will see an error on which non-table-column fields the model was not trained on.
Note that, with v32+, signatures are compatible with all Semi-structured models. Signature fields can now be trained and are eligible for Field ID automation. To learn more, see Checkboxes and Signatures.
Compatibility with Model Upload
Just like with model deployment, model upload will fail if the candidate model is not compatible with the live layout version. To ensure compatibility when uploading a model from another instance, upload and deploy the layout version first.