A notable feature of the revised 1980 index number series was the inclusion of 18 items from the SSI sector, for which the office of the Development Commissioner of Small-Scale Industries (DCSSI) could ensure regular supply of data. The production data for the small-scale sector were included only from the month of July 1984 onwards; prior to this the production data from the directorate general of technical development (DGTD) for large and medium industries alone had been utilised. For the period April 1981 to June 1984 in respect of these 18 items, average base year (1980–81) production as obtained from DGTD was utilized. From July 1984 onwards, combined average base year production both for DGTD and DCSSI products was utilised. The weights for these items were based on ASI 1980–1981 results and no separate weights for DGTD and DCSSI items were allocated in the 1980–81 series.
The next revision of IIP with 1993–94 as the base year containing 543 items (with the addition of 3 items for mining sector and 188 for the manufacturing sector) has come into existence on 27 May 1998 and ever since, the quick estimates of IIP are being released as per the norms set out for the IMF’s SDDS2, with a time lag of six weeks from the reference month. These quick estimates for a given month are revised twice in the subsequent months. To retain the distinctive character and enable the collection of data, the source agencies proposed clubbing of 478 items of the manufacturing sector into 285 item groups and thus making a total of 287 item groups together with one each of electricity and mining & quarrying. The revised series has followed the National Industrial Classification NIC-1987. Another important feature of the latest series is the inclusion of unorganised manufacturing sector (That is, the same 18 SSI products) along with organised sector for the first time in the weighting diagram.
Recent revision of IIP released by CSO with 2004–05 as the base year comprises 682 items. As per chief statistician T C A Anant, this index shall give a better picture of growth in various sectors of the economy, because it is broader and includes technologically advanced goods such as cell phones and iPods. The previous base year (1993–94) was not usable as the list contained an array of outdated items such as typewriters and tape recorders.