Landsmanshaften were societies that were based on connections to the villages of the Old Country. Most of these societies disbanded between the years 1960 to 1980. As their founding was registered with the State of New York, so too their disbanding went through the state government. The records of these societies, which included their papers and records, were given to New York State, which then passed them on to YIVO.
Jerry Seligsohn spent many months at YIVO, searching for the records of defunct Belorussian landsmanshaften societies. Many of these records are hand written, in either English or Yiddish. Mr. Seligsohn did his best to interpret the names, and make the information available on the Internet. However, as with any other research, it is best if you can check the original records for yourself.
When YIVO received these records from the state government, they sorted them into boxes, and assigned them an "RG" classification. To find and record the names within this collection is not a simple matter. They must be dug out of various files, and from the various records within. The usual best source of names are the dues lists. Sometimes the names appear in alphabetized printed lists of celebratory publications. The stubs of burial receipts can be another source of names. But these records must be manually searched, and then begins the process of locating the names. To expect YIVO to do this for you is beyond their capacities.
If you search these records, you might locate an old address of your ancestor. Knowing a name and an address may allow you to gather additional information by employing the standard methods of genealogical records research.