Whether the cantonal court could declare the appeal inadmissible as late without hearing the appellant on the timeliness issue.
Because the file and new documents created a genuine doubt about late filing, the appellant had to be heard before an inadmissibility ruling could be issued.
Under the right to be heard, a party must be allowed to address a potentially decisive procedural issue when the court is not fully certain. Where the documents do not clearly establish tardiness, the authority must invite observations before deciding.