Another data point on the General Motors ignition recall timeline has been filled in with the latest revelation that test drivers for the car maker’s Cadillac division spotted the problem eight years ago, possibly leading to a hush-hush design tweak in the switch.

According to the Wall Street Journal, newly uncovered documents related to the defect that has led to at least 13 fatalities and the recall of 2.6 million vehicles show that test drivers of the pre-production 2007 Cadillac SRX noted that the vehicle’s ignition switch could turn off — disabling power steering, brake-assist, and air bags — if bumped by the driver’s knee.

This may explain why, in April 2006, a GM engineer quietly gave the go-ahead to the third-party manufacturer of the defective switch to update the design to prevent this problem; an issue the car company had been made aware of as far back as 2001.

The problem with that redesign is that GM did not change the part number. Thus, the new, more robust ignition switches have been stocked alongside the old defective ones.

The engineer in charge of this ignition switch is believed to be one of the two GM employees recently suspended by the company.

As we mentioned yesterday, GM is attempting to use its recent bankruptcy to shield itself from the new lawsuits related to this defect, as the problematic switch was a creation of the “old GM” from before the company was bailed out when the economy collapsed.

Want more consumer news? Visit our parent organization, Consumer Reports, for the latest on scams, recalls, and other consumer issues.