CBI, which has registered a preliminary enquiry (PE) after receiving a reference from CVC, could not finalise its report in three months time frame because of "complex nature" of the case, agency sources said.
They said a three-month time limit, which expired on August 31, is a flexible one and they can seek more time from the anti-corruption watchdog.
In its request seeking more time, the agency is understood to have intimated CVC about the alleged prima-facie irregularities it has found about the beneficiary companies.
Meanwhile, CBI teams are camping in Chhattisgarh and Jharkhand and examining officials concerned of the companies under the scanner of the agency.
A CBI spokesperson had clarified that no raids were taking place and the teams were there as part of the agency's ongoing PE into the alleged coal scam.
At least 10 companies, which benefited from the coal block allocation, are under CBI scanner for alleged violation of norms, they said.
The sources said that the agency is likely to register cases in different batches and nearly eight companies could be booked in the first set.
They said CBI has already questioned senior bureaucrats who were overseeing allocation of coal blocks during 2006-09.
Meanwhile, the agency is also taking into cognisance the Comptroller and Auditor General report on alleged coal blocks issue which was tabled in Parliament recently.
The sources, however, made it clear that CBI would not be going into policy issues but will limit its role to aspects where criminality could be established.
