RegDCP - 6:11 am on Sep 6, 2012 (gmt 0)
Yes you are right but it is progressive, not retroactive.
When the PR algos are changed the new "rules" come into effect, but they do not overwrite the old.
With the new rules, PR is calculated on the basis of relevance, which was not in the original algos. This was changed in the Mayday update.
There is also no correlation now between PR and SERPs.
With Penguin the linking factors were again turned on, the linking profile for each website calculated retroactively, and then the linking factors turned off again.
You might not thing PR is a factor in Penguin but it explains exactly hat has happened.
It is the keywords that decide the penalty, but it is not based on the percentage of their use, as is supposed by a lot of people.
"Artificially" boosted rankings would be determined by links on non-relevant pages, and the anchor text used on these non-relevant links, would form the basis of the penalties.