The sObjectType column in the MatchingRule table is 40 characters. This means the sObject API name can be up to 40 characters. A user is able to enter 43 characters in the field. Why is this possible?
The standard length of the sObjectType field is 40 characters. A Custom SObject name can be a maximum of 43 characters. This is because the first 40 characters of the name are chosen by the user and three characters are automatically added by Salesforce. Salesforce adds __c to the name since it is a custom Object. The sObject name replicates to this field in the RecordType object once the user creates a Record Type in an sObject.