Steraks Base AD not displaying properly.

Example- Steraks Gage on Gangplank at level 18 will give him 32 Base AD. But if i buy 2 Steraks, They both will say they give base 40 AD. Ive checked, and they both still only give 32 Base AD a piece. The Number will change with the more steraks i buy. All of them still give 32 ad each, no matter how many i buy. 1 sterak-32 ad 2 sterak-40 ad 3 sterak-47 ad
4 sterak-54 ad
5 sterak 62 ad