How can you distinguish bewteen changes to a site that invalidate the label and changes that do not?
Unfortunately, you can’t tell in general. A client may choose to trust a label even if the contents of a document have changed since the label was created. A labeling service that is confident its label will still be valid even if changes are made to the contents, perhaps because it trusts the author, can omit the cryptographic checksum from the label. In that case, the labeler is strongly encouraged to include an expiration date in the label.
