You are confusing the Insolvency Register with your credit reference agency files.
You will be removed from the REGISTER within 3 months of the certificate being issued. Some come off almost right away, some wait the full three months, depending upon who picks up your file at the Insolvency Service.
Your credit reference files will start to clear up at the 6th anniversary of the start of the IVA, provided that the certificate has been issued and you are off the Insolvency Register. So, by the time you get it the 6 years will have passed and the CRA's will start the clear up once you are off the Insolvency Register.
The actual defaults, if correctly dated, will fall off at 6 years anyway -- so that should already be happening --- the biggie, though, is the IVA itself, which will fall off as mentioned above.
Have a read here:
http://debtcamel.co.uk/repair-credit-record-iva/
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014