Section 18 (1) (a) & (b) says”…… shall be entitled to take credit of input tax in respect of inputs held in stock ….”. So, to me, the ITC is available only in respects of Inputs.
Thus, the words “capital goods” are missing in (a) and (b) while The words “and Capital goods” are added in 18(1)(C )& (d).
Again , “Inputs”, as per section 2(59) “means any goods other than capital goods used or intended to be used by a supplier in the course or furtherance of business”
Summarily, to me, capital goods are categorically excluded for claiming ITC in the case of Registration taken voluntarily or on exceeding prescribed limits.