SQL Server 2012 :: How To Group Near Duplicate Records Under A New Common Field

I've inherited a table of members that has the following structure:

CREATE TABLE [dbo].[dimMember](
[dimMemberId] [int] IDENTITY(1,1) NOT NULL,
[dimSourceSystemId] [int] NOT NULL CONSTRAINT [DF_dimMember_dimSourceSystemId] DEFAULT ((-1)),
[MemberCode] [nvarchar](50) NOT NULL,
[FirstName] [nvarchar](250) NOT NULL,
[LastName] [nvarchar](250) NOT NULL,

[Code] ....

Based on the way the data loads into the table there's a possibility of some records being near duplicates of each other. For example, we can have a member that has records that have the same first name, last name, SSN, but different addresses, membercodes, subscribercode etc... This can happen in pretty much any variation thereof.

What I want to do, is add a new column and use that to group the similar records under based on comparing on several columns. By this I mean, if a member matches 4 of the 7 values below with another member, we would group these:

First Name (1st 3 characters)
Last Name
DOB
CurrentAddress1
MemberCode
SSN
SubscriberCode

I'm at a loss of how to structure the SQL to update the new column in the table.