Using a false SSN to work...my immigration lawyer told me directly that since the acquisition and use was NOT for the benefit of immigration in any way, it would not affect the adjustment of status...and it did not in our case, but you are talking about a much longer period of time in use..

The only other part that might affect this is where immgration asks if you have been arrested/convicted of crimes....if there has been and legal type procedings based on the false SSN...or a IRS Audit/inquiry..you may have to disclose this and that would be considered...if nothing has happened, then you can honestly say no arrest/conviction and they would probably never know about it.