SQL Server Primary key / clustered index design decision
You are correct to separate "clustered index" from "primary key":


A clustered index is the organisation of data on disk is better if

narrow
numeric
increasing (strictly monotonic)

The primary key identifies a row


Note: GUIDs make poor clustering keys

In this case, with the surrogate column, the table has 2 candidate keys:


ProductHistoryID
ProductNo + CreatedDateTime 


Assumed convention states that the ProductHistoryID becomes the PK, but you can leave the PK on (ProductNo, CreatedDateTime): it will just be non-clustered. Which leads to indexes:


clustered index should be on ProductHistoryID
unique non-clustered index on (ProductNo, CreatedDateTime)


Example

CREATE TABLE Product (
    ProductHistoryID int NOT NULL IDENTITY (1,1) NOT NULL,
    ProductNo ...
    CreatedDateTime ...


then you a choice of

    CONSTRAINT PK_Product PRIMARY KEY CLUSTERED (ProductHistoryID)
    CONSTRAINT UQ_Product UNIQUE NONCLUSTERED (ProductHistoryID)


or

    CONSTRAINT PK_Product PRIMARY KEY NONCLUSTERED (ProductNo, CreatedDateTime)
    CONSTRAINT PK_Product UNIQUE CLUSTERED (ProductHistoryID)


Also, the pattern you have is a "type 2 Slowly Changing Dimension"