2013 Grammys Dress Code -- Underboob 'Barely' Met CBS' Standards

Katy Perry's giant TA-TA's ... Alicia Keys' underboobs ... Kelly Rowland's twins ... turns out they were all given the stamp of approval from CBS -- despite the network's previously harsh warning to keep the nakedness to a minimum.

Despite these revealing outfits -- and several more -- a rep for CBS tells TMZ, "All wardrobe selections passed our standards, if only barely."

You'll remember … CBS issued a memo urging everyone in attendance to cover up or else -- saying in part: "Please be sure that buttocks and female breasts are adequately covered. Thong type costumes are problematic. Please avoid exposing bare fleshy under curves of the buttocks and buttock crack."

If this is the music biz covering up ... count us in!