iPrint audit file

When looking at the print jobs in the audit.csv file, the page count is not always accurate. 

In many instances the pages printed at the printer is less or more than indicated in the audit file. 

What impacts these numbers and how can this be fixed to provide more accurate information. 

Kind of file being printed ? pdf.. word... exel.. .txt etc..

Machine OS from where the job is being sent or the printer driver. 

Anyone else had similar results and how best to resolve this if we have a lot of different printer makes and models. 

Thanks