This appears to be another example of changing the model number after the slide rule had been manufactured.  Specimens with both 1426 and 44CB-260 model numbers exist but I'm sure Teledyne-Post never sold this rule under any model number other than 44CB-260.  The rule illistrated in the catalog appears to have been marked model 1426 but "1426" has been removed from the illustration.  

1972 Teledyne-Post Slide Rule Catalog.  Model 44CB-260 is the first item listed.

Top:  Teledyne-Post 1426.   Date code "^UD" (April 1970).  Date codes at least as early as August 1969 exist. Middle: Teledyne-Post 44CB-260.   Date code "^UD"  (April 1970).  This is not a mistake.  Both rules have the same date code.   Date codes like this make me think that the date code represents when the blank was made.  The markings may have been added to the blank several years later. ( Another possibility is that the rules may have been made during the same month but the Teledyne Post markings added years apart.  I tend to reject that hypothesis.  Some Hemmi rules have date codes as much as five years earlier than Hemmi officially announced the creation of the model.  Hemmi was certainly working with several-year-old blanks.)  Bottom: Backs are identical.