The Old UCSC Genes track shows genes from the previous version of the UCSC Genes build, which was built with GENCODE v44 models. See the description page for more information on how the new GENCODE v45 track was built.
The new release has 277,081 total transcripts, compared with 276,905 in the previous version. The total number of canonical genes has increased from 70,116 to 70,711.