The really interesting question is why the immediate raising of the threat level? Unless you're planning to keep it at that level forever, old surveillance doesn't put any particular time frame on planned attacks or even if an attack is planned. It also doesn't do anything about any other places that might have been checked out that you don't necessarily know about.
That's where the "multiple sources of information" may come in - information from other sources about plans for attacks over the next 3 months or so. In that case, any place that was the subject of extensive surveillance even years ago would be an obvious possibility for a new and imminent attack and worth extra protection.
My guess is that something like that is what happened.
I agree. It's been stated, but the dems are trying desperately to drown out the fact that this information was recently *updated* by the terrorists and corroborated with *new* information.