NBC ADDS MTM'S 'DUCK FACTORY'
NYTimes - almost 33 years
-founded by Grant Tinker, and since Mr. Tinker is the current head of NBC-TV, it might seem a bit touchy for the network to stock up heavily on MTM products. On the other hand, MTM has an exceptionally good record for quality series, and NBC would be daft not to do business with the studio. In any event, another MTM series, ''The Duck Factory,'' is