셨군요/셨(더)군요. why use '더' ? just feeling difference. if use '더', emphasize the meaning. But, actually, no meaningful to distingulish 셨군요 from 셨더군요.
셨=polite+past tense
Do=하다. Do=하시다(polite). Did=했다. Did=하셨다(polite)
Ex. 하셨군요= you did it(polite). 했군요 = you did it(less polite)
Verb+군요, Verb+셨군요