This contribution is a study on SEI processing order (SPO) SEI message use cases. In this document, several SPO SEI message use cases are presented. These use cases are especially focused on broadcast applications with Set-Top-Boxes (STBs) as the decoding examples. Some limitations of current existing SPO SEI message design, which is detailed in “SEI processing order and processing order nesting SEI messages in VVC (draft 7)” JVET-AG2027, have been highlighted. The modification on top of the existing SPO SEI message design, as proposed in JVET-AG0105 and its follow-up in JVET-AH0134, is further examined and explained. The advantages with the modification on top of the current existing SPO SEI message design are discussed in the scenario of broadcast STBs that have been shipped into use as different generations. This contribution document serves as an assistant document for JVET-AH0134.