The one extra userpic per continuous year of paid time isn't historical. The 1 per 3 months of paid time is, but not the 1 extra for each year of continuous paid time. That one you only get from this point forward.
So, for example, I...
Bought 6 months of paid time in 2004
Bought 12 months of paid time in 2005
And am currently a paid member
I would get:
2 loyalty userpics for the 6 months of paid time
4 loyalty userpics for the 12 months of paid time
For a total of 6 extra userpics.
If I bought ANOTHER 12 month paid account today, then I would get 5 more -- 4 for the one-every-three-months and a bonus one for the year of continuous time.
I can't suggest any wording tweaks right this second, but the first and last two paragraphs need to be edited to clarify this.
Thanks! You guys are awesome!