Devil's Advocate
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I remember reading that 737 aircraft delivered with eyebrow windows had never been certified for use without them and thus were ineligible to have them structurally removed after delivery. However, it's quite possible that a third party vendor managed to receive approval for removable non-structural plugs or filters for blocking excessive sunlight that could interfere with interior visibility.The eyebrow windows were removed in 2005, about 8 years after the 737NG entered service. I think most of the NGs were probably retrofitted to remove them.737s had the eybrow windows until the model 737-600 AFAIR. Starting from 737-700s those were gone.