I think there is also the consideration of unlicensed assemblers assembling PC's from scratch, from components sought from different sources. That I think comprises the crucial part of the grey market in PC sales. I know I bought my first PC from a guy called Rajan, who sourced components from Malaysia and assembled the PC in his now bustlin' shop in Goregaon. He also served as my technician for a good many years. If he was to be believed, most household consumers in India in the '90's were buying desktops from hardware assemblers, who also installed pirated software on their systems and doubled up as technicians, because they were so good.
If components were being sourced cheaply from local manufacturers, they were liable to underwrite sales or not report them at all. If they were being imported in mass quantities, records malfeasance would be more difficult, but still possible. With the exception of imports, it would be impossible to factor all these into GDP because they were not final produce, rather sub-components for a larger, finished good. Having some, previous exposure to the extent to which Indian companies will underreport sales for tax-evasion, I'd hazard a guess that the gray market for computer goods in India comprises a significant, if not preponderant, percentage of the total market.