The following resourcesIds on the terraform not scoped to the specific gateway ID's that they belong to.
aws_api_gateway_model
aws_api_gateway_resource
This means the underlying resources may generate the same resource and be replaced on update if the object renders with the same sub-id in AWS.
Practically - this means that if you have two api_gateway's with the same resources/routes in the same AWS account/region, terraformer will only save the state for the last imported api_gateway missing the other's resources.