Complex sentence: To cut costs, on most Rev.2's and all Rev.3's, the engraved buttons were replaced with unlabeled buttons and, in lieu of the engraved words or symbols on the buttons, the names of the buttons were printed on the front panel.
Split into simpler sentences: To cut costs, later Rev.2's and all Rev.3's replaced the engraved buttons with unlabeled buttons. In lieu of the words or symbols engraved on the buttons, the names of the buttons were printed on the front panel.