not able to see earlier measurement documents

I have an Equipment in reference to which documents are created since 2005 in its history.

and each time delivery is created measurement documents gets created, which can be seen in reference to existing measurement points in normal scenario.

but for a particular equipment last measurement documents available are of year 2014 and 2013 only. All the earlier measurement documents cant be seen in Equipment or in IK17.

Are they deleted or can be seen somewhere?