ISRC Encoding Query

I’ve come to the discovery that I can help reduce the large amount of duplications by extracting ISRC’s from my CD’s and adding them.

However I just want to clarify something, reading on the Wikipedia article it mentions:

ISO 3901 was completed in 1986. In 1988, the IFPI recommended that its member companies adopt ISRCs for music videos. In 1989, the ISO designated the IFPI as the registration authority for ISRCs. The IFPI, in turn, delegated part of the administration of ISRCs to several dozen national agencies, which allocate ISRCs to both record companies and individuals.[2] The national agencies began assigning ISRCs for music videos in August 1989.

The Japanese recording industry began encoding ISRCs on audio CDs in November 1989. The IFPI and the Recording Industry Association of America (RIAA) then developed detailed recommendations for this practice, and for ISRC assignment in general. The IFPI adopted the recommendations in March 1991 and they went into effect for IFPI members on 1 January 1992.

So would this mean that any CD produced before 1/1/1992 likely does not have the ISRC’s encoded? I’ve found a few compilations that I have from 1991 and 1990 (for example) have this information missing.

Or 1989, for Japanese-produced CDs. As I understand it, even CDs produced today may not have ISRCs encoded if the publishers/artists didn’t request one. I imagine this would be common in indie or self-published CDs.

Indeed - I kinda assume it with self-pressed/released/independent labels, but not from companies such as EMI, Telstar or Virgin; of which these compilations were from

One unrelated interesting thing to notice is that the year (two digits) on Japanese ISRC is almost always the recording year.

It used to be sometimes not the case for other country ISRC where it is more often the ISRC registration year (less useful).
But I hopefully see now more and more recording years in French ISRC too.