You probably misread the seating diagram. (I've done it myself!)
Forward facing seats when travelling to Paris:
Coach 1 (Standard): 15 to 24, 31 to 34, 41 to 44, 61 to 64, 71 to 74
Coaches 2, 3, 4 & 5 (Standard): 45 to 87
Coaches 7 & 8 (Leisure Select / Business Premier): 15, 17, 18, 35 to 51, 65, 67, 68, 75, 77, 78
Coach 9 (Leisure Select / Business Premier): 25, 27, 28, 35, 37, 38, 45, 47, 48, 55, 57, 58
Coach 10 (Leisure Select / Business Premier): 21, 23, 24, 31, 33, 34, 41, 43, 44, 51, 53, 54
Coaches 11 & 12 (Leisure Select / Business Premier): 11, 13, 14, 21 to 44, 61, 63, 64, 71, 73, 74
Coaches 14, 15, 16 & 17 (Standard): 11 to 44
Coach 18: 25 to 28, 35 to 38, 45 to 48, 65 to 68, 75 to 78
Forward facing seats when travelling to London:
Coach 1 (Standard): 25 to 28, 35 to 38, 45 to 54, 65 to 68, 75 to 78
Coaches 2, 3, 4 & 5 (Standard): 11 to 44
Coaches 7 & 8 (Leisure Select / Business Premier): 11, 13, 14, 21 to 34, 61, 63, 64, 71, 73, 74
Coach 9 (Leisure Select / Business Premier): 21, 23, 24, 31, 33, 34, 61, 63, 64, 71, 73, 74
Coach 10 (Leisure Select / Business Premier): 25, 27, 28, 35, 37, 38, 45, 47, 48, 55, 57, 58
Coaches 11 & 12 (Leisure Select / Business Premier): 15, 17, 18, 35 to 54, 65, 67, 68, 75, 77, 78
Coaches 14, 15, 16 & 17 (Standard): 45 to 88
Coach 18: 15 to 24, 31 to 34, 41 to 44, 61 to 64, 71 to 74