Tds not claimed-can we rectify u/s. 154 & claim refund ???

beforehand, please ensure that the amount mentioned in 26AS, was included in the taxable income of the assesee :) 

mere claim of tax from 26AS is not your duty but to compile the taxable income also with 26AS

such cases are suitable cases to be selected for re-assessment or scurtiny where the assesee is not aware of his income or tax deducted and rush to file incomplete data to department.