NCBI’s Reference Sequence (RefSeq) FTP release numbers will increment to 200 for the next release and skip over the numbers 100-199. The current, March 2020 release, is release 99. The next bi-monthly release in May 2020 will be release 200. This change is to avoid overlapping with the release numbers of the completely independent RefSeq annotation releases for the eukaryotic genomes we annotate, which are currently in the range 100-109, for example Mus musculus Annotation Release 108.
The RefSeq FTP release number is encoded in the file RELEASE_NUMBER, under the main RefSeq release FTP directory. It is used in some statistics files and in the name of some companion report files in the following sub-directories on our FTP site: release-notes/, release-catalog/, release-statistics/.