You're quite right, Rae. It's just the rear that's 'A'. You've earned (my contribution to) your pension today!
http://www.pirelli.com/tyre/ww/en/news/2013/04/24/new-pirelli-angel-gt-sport-touring-tyre-is-number-one-in-its-segment-for-mileage/Front
120/60 ZR 17 M/C (55W) TL
120/70 ZR 17 M/C (58W) TL
110/80 ZR 18 M/C (58W) TL
120/70 ZR 18 M/C (59W) TL
Rear
150/70 ZR 17 M/C (69W) TL
160/60 ZR 17 M/C (69W) TL
170/60 ZR 17 M/C (72W) TL
180/55 ZR 17 M/C (73W) TL
180/55 ZR 17 M/C (73W) TL (A)
190/50 ZR 17 M/C (73W) TL
190/50 ZR 17 M/C (73W) TL (A)
190/55 ZR 17 M/C (75W) TL
190/55 ZR 17 M/C (75W) TL (A)
190/55 ZR 17 M/C (75W) TL (D)
160/60 ZR 18 M/C (70W) TL
(A) Two layer structure for better stability
(D) OEM equipment on the new Ducati Multistrada 1200 S Granturismo