1. Electronic documents: With the popularity of electronic documents, many companies and institutions may choose to use electronic formats when issuing announcements, notices and other documents. Electronic documents have no physical seal.

2. Scanned copy: If this notification letter is scanned, it may be because the physical seal was not scanned during the scanning process. Or the quality of scanned documents is poor, resulting in unclear seals.

3. Not stamped: It is also possible that the document was accidentally stamped when it was made.