[This is preliminary documentation and subject to change.]
When the Microsoft WinSNMP implementation receives traps from an entity operating under the SNMPv1 framework, it translates the traps to the SNMPv2C format. Therefore, when SnmpRecvMsg delivers a trap it is always in the SNMPv2C format. RFC 1908, "Coexistence between Version 1 and Version 2 of the Internet-standard Network Management Framework," specifies the rules for translating from the SNMPv1 to the SNMPv2C trap format.
A WinSNMP manager application can check the last variable binding entry in a variable binding list to determine if the entry is a trap translated from the SNMPv1 to the SNMPv2C format. If so, the last variable binding will always be equal to the value "snmpTrapEnterpriseOID.0".