When model data is encoded in GRIB, the dataset schema is lost. So is an unambiguous identification of the the schema variables. To deal with these problems, GRIB reading libraries probably make assumptions that may not be valid for all datasets.
Problems with external tables make BUFR/GRIB not suitable as long-term storage formats. To solve this, there must be a foolproof way for
reading software to know what tables the writing software used, and there must be an authoritative registry of tables.