• If you enter a retired rs number into the “Search for IDs” search text box on the dbSNP home page, the response page will state that the SNP has been merged, and will provide the new rs number and a link to the refSNP page for that new rs number.
• You can retrieve a list of merged rs numbers from Entrez SNP. Just type “mergedrs” (without the quotation marks) in the text box at the top of the page and click the “go” button. You can limit the output to merged rs numbers within a certain species by clicking on the “Limits” tab and then selecting the organism you wish from the organism selection box. Each entry in the returned list will include the old rs numbers that has merged, and the new rs number it has merged into (with a link to the refSNP page for the new rs number).
• You can also review the RsMergeArch table for the merge partners of a particular species of interest, as it tracks all merge events that occur in dbSNP. This table is available on the dbSNP FTP site, a full description of it can be found in the dbSNP Data Dictionary, and the column definitions are located in the dbSNP_main_table.sql.gz, which can be found in the shared​_schema directory of the dbSNP FTP site.
• You can locate the partner of a split refSNP only by using SQL:

SELECT  *
  FROM [human_9606].[dbo].[RsSplitArch] where rs_2_split = 26
rs_2_split  rs_new_split      split_build_id    create_time last_updated_time
26    78384355    132   2010-08-19 23:38:00     2010-08-19 23:38:00