The 1989 Best set finally became important a decade after issue when it was belatedly realized it included the first and only official 1980's card of Sammy Sosa and a rookie year card of Ken Griffey Jr. Randy Johnson too.

From 1987 to 1990 Donruss produced a comprehensive mid-season "Best" set. The first 1987 release was named "Opening Day" as it only had players who were in the starting lineup for the first game of that season. Why, for example, Mark McGwire and Nolan Ryan are not in that set.

The 1988-90 sets were named "Best Of". But since these factory boxed sets were mostly distributed through retail outlets like Wal-Mart rather than card dealers, they didn't get 'hobby recognition' that the similar traded sets did at the time and weren't included in the monthly price guides.
But now it's obvious that Donruss BEST singles are MUCH TOUGHER to find than the regular issues from these years.