15/16 I am assuming annual salary was also £170k, therefore he would be entitled to only £30k AA (170-150 = 20/2 = 10 to taper from 40 leaving only £30 for 15/16.
As he made he made gross contribution of £10k in 15/16 should he not only have £20k left to c/f to 16/17 to add to avail AA of £30 resulting a max £50k for this year.