There was no Wildcat Special Deluxe. Wildcats In 66 came as Wildcats and Wildcat Customs.
There was a Buick Special Deluxe in 66 which is an A body. Wiildcats were generally B bodies. If it has "Wildcat" on an air cleaner decal it does not mean it is a Wildcat model.
131 A would be blue interior and I think the A would likely denote a bench notchback seat. Perhaps you can verify this.
The others are accessory codes :
W = Tinted windshield
2X= ST 300 trans
5Y = Deluxe Seatbelts
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