Somewhat related information after re-reading:
Held Items are 50%/5%/1%, the 1% occurring in dark grass for all Pokemon that have it.
With Compoundeyes as your lead, it's 60%/20%/5%.
rand(0,99) = upper32*100>>32
0-49 // 50-54 // 55
0-59 // 60-79 // 80-84
Although it's not present in this narc, for items it is relevant to this subject