We do not have any additional information on how any particular SIC or DNUM designation was decided by Compustat and CRSP. We do know that determining the primary industry is not always straightforward and it is often open to interpretation.
For this case, SICs 1400 and 2800 are related industries, and a company could easily be involved in both industries.
One thing to know is that there are differences in how these datasets were constructed that will make some SICH and HSICCD designations completely different simply because so many companies are covered and the industry designations come from different sources (i.e., there are surely anomalies and mistakes, such that searching for differences in HSICCD and SICH). SICH does not solve this problem.
Also, more than one version of the company may be involved.
For example, let's consider the company 'Koppers'. Looking at the company history on their website (KOOPERS.COM) shows:
Koppers has a rich tradition in manufacturing, carrying forth a name that has stood for quality and dependability through parts of two centuries. The current company, Koppers Inc., was created as Koppers Industries, Inc. in December 1988 when it acquired some of the assets of what was then called Koppers Company, Inc., in a management-led leveraged buyout. One of those assets was the "Koppers" name. The company changed its name from Koppers Industries, Inc. to Koppers Inc., in February 2003.
PERMNO= 22170 for KOPPERS CO in CRSP stopped trading in 1988, while KOPPERS INC still exists, but it may not have a publicly traded stock at this time. Further research by yourself or someone at CRSP or Compustat would be needed to determine exactly how these companies are related.
If you use our company lookup feature at WRDS Tools and enter 'KOPPERS' as a company name, Compustat shows three entries and the last seems consistent with the CRSP SIC.
|Company Name||CNUM||Ticker Symbol||GVKEY||DNUM||NAICS|
|KOPPERS HOLDINGS CORP||50099Y||6502B||21465||2400||321|