Manafort has had 8 months warning to cover his tracks. Manafort has 5 homes, just one was raided, that we know of.
That being said , the raid happened on July 26th and this explains the second grand Jury Mueller created in DC less than a week after the raid and his hiring of attorney Greg Andres on August 1st, who used to work for the Department of Justice.
He was deputy assistant attorney general in the criminal division, where he oversaw the fraud unit and managed the program that targeted illegal foreign bribery.
So whatever they got from the Manafort raid is solid and promoted creating a DC Grand Jury and and hiring a foreign bribery expert for crimes committed in DC. Manaforts house that was raided is in Alexandria, Va., where the first Grand Jury was created a couple months ago.
So putting the pieces together whatever they found in Virginia is tied to crimes committed in DC involving foreign bribery.
Since May the Whitehouse has been refusing to hand over documents pertaining to Michael Flynn requested by congress.
Trump White House Refuses to Give Key Flynn Documents to Congress ? Mother Jones
Why would the Whitehouse refuse to give documents over pertaining to Flynn, an employee that got fired for lying?