In Lovely but Lethal, Viveca's prints should be on the magazine that she wrote on to offer Carl more money. Columbo looks at it closely enough to notice that the figures were written with a make-up pencil, but why doesn't he see or check for any prints?
And 2 telephone problems....
In How to Dial a Murder...couldn't they check the phone records to see if Dr. Mason had called from the examining room when he was having his test done?
And on the same note...in Old Fashioned Murder...couldn't they check the phone records of the museum to see if Milton Schaeffer actually called his brother from there?
And I always thought Dr. Mason was quite lucky that there was a telephone in the examination room, that he could get an outside line, and that he knew the code for an outside line. And that the doctor would leave him alone at exactly 3:00. Also, what if Charlie wouldn't have answered the phone? It's not his house, not his phone...I wouldn't have answered it.