The reason why it appears the updated field labels are not displaying on the Marketo Landing Page is that the field labels that are being displayed are not the field labels that were edited. The field labels that are being displayed is what is defined in the Visibility Rules of the fields.
To ensure that the updated field label is displayed on the Marketo Landing Page, the field label in the Visibility Rules must also be updated
https://docs.marketo.com/display/public/DOCS/Dynamically+Toggle+Visibility+of+a+Form+Field