The mod is a two-part mod. The basic mod covers the seating and signage. Some aircraft have gotten the second part of the mod covering the new gray PSUs and the fluorescent white signage. Many of the MD
-88s still don't have the new PSUs yet. Was the 757 you flown on an ex-Song 757? The Song mods did not include PSU updates. Eventually, the MD
-88s with the black PSUs and the 757s with the brown PSUs will get the update.
I wonder if there will be any updates on the newer 757s with the white PSUs? The white PSUs on those 757s are the 737NG-style, which are more modern than those with the brown PSUs.