The Old UCSC Genes track shows genes from the previous version of the UCSC Genes build, which was built with Gencode v29 models. See the description page for more information on how the new GENCODE track was built.
The new release has 193,749 total transcripts, compared with 197,782 in the previous version. The total number of canonical genes has increased from 49,948 to 64,792. Comparing the new gene set with the previous version: