Verily that is what I wrote, but it is not the case (pun accidental). The chamfered corners have horizontal slots. The top side edges are indeed provided with (seemingly) pressed-in louvred panels, rather than the same kind of open slots. This press-in could have been Apple engineers' desperate late response to the fiat against an internal fan, as raised by tomlee59.
When I first held the bucket to the light some days ago the louvres appeared simply to be translucent plastic grooves. However, your question prompted me to go back to where I have been handling the bucket intermittently for several days, and to look with an angled light source. Sure 'nuff, there are slotted openings at the rear edges of what I had wrongly taken to be mere incuse grooves. The bucket defiantly displays the Apple press-in logo. and the legend 'Macintosh 512K', as well as the moulded-in P/N 810-0374- and stamped-on 630-5139-A.
With the acute vision that hindsight engenders, the intended internal fan's position could be thought to be reflected in the moulding of the bucket, but in a position closely analogous to that of the SE/30's fan. The signatures in that part of the bucket would have been casualties of the fan's positioning, as the signature of Steven Jobs near the centre is already (and perhaps, ironically).
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