What's the actual difference? Isn't the UD (Unanimous Decision) a "united" decision, where all the referees agree who is the winner? What's then the meaning of PTS?
PTS means a result on points, where a UD statement would be inappropriate. For example,
historic fights may not have the judge's scores available in record, and therefore it is unsure whether a UD is what occurred
a number of regions had only one person deciding points in their history, and UD implies more than one person
any other situation where a decision on points was made but where there is not enough information to say it was UD, MD or SD (unanimous, majority or split).