Most common reason for PR downgrade ?

Hi, got a blog downgraded from PR3 to PR1

Tell me if any of these can be the guilty ones;

A) 1 MONTH AGO
*- blasted 1,5k with SB directly to my blog, using the same email always (usually I don't, but for this campaign I needed to be contacted if necesary)

B) 5 MONTHS AGO
*- duplicated internal content (deep pages containing = article as home)

C) 6 MONTHS AGO
*- Did several SB blasts and later did not continue link velocity (these blasts took the blog from PR2 to PR3..)

What are commons reasons for PR downgrade ?

Thanks