That cannot be the reason buddy as then u would not have got amazon prime video benefit too. Each benefit can b claimed once for a particular plan or on a RMN linked with broadband, dth or prepaid/postpaid connection . So if u have opted for Rs. 999 broadband plan and claimed free prime video subscription then same cannot be claimed again even if upgrade to any other plan which offers this benefit (unless mentioned in terms and conditions). If u have same RMN registered for say broadband and DTH account then again u can claim benefit under applicable plan once on each account.
Right now as u have opted for airtel black plan hence both benefits r applicable on ur account as these do not come under any separate DTH or Broadband or Mobile plan benefits
So u have not claimed the free 2 year prime video benefit received under earlier 200 mbps broadband plan, if so then same will stand cancelled now as u have opted for airtel black and now u will be eligible for this benefit under new plan. Had u opted for it earlier then u would have got opportunity to get this benefit twice