Considering you most likely have already looked at the data file, you may have noticed a major change in the TSUSA code pattern. The abbreviation TSUSA stands for "Tariff Schedule of the United States Annotated." We use this pre-1989 term synonymously to also include the current "Harmonized Tariff Schedule of the United States Annotated" (HTSUSA) used for imported products and the "Schedule B" used for exports.
Hopefully, you also noticed the hierarchical NAME pattern. Although not the legal description it certainly eases data retrieval when selecting by the groupings, e.g. Groundfish, Tuna, Shrimp, etc. which have numerous codes associated with the products.