Seal was really just used to inform consumer that the game would work on Nintendo systems (properly licensed by Nintendo). It didn't really deal with quality considering their are plenty of shitty NES games.
"The Nintendo Seal of Quality is still used today, with all Nintendo DS and Wii games bearing it on their packaging. However, it has recently been changed to read simply Official Nintendo Seal rather than Official Nintendo Seal of Quality.
When the Official Nintendo Seal of Quality was used, the meaning of the seal was explained as follows:
This official seal is your assurance that Nintendo has approved the quality of this product. Always look for this seal when buying games and accessories to ensure complete compatibility with your <insert name of Nintendo system here>.
Basically this meant that the cartridge works in the named hardware, it had nothing to do with the written quality of the software.
The current Official Nintendo Seal is explained as follows:
The official seal is your assurance that this product is licensed or manufactured by Nintendo. Always look for this seal when buying video game systems, accessories, games, and related products.
Aside from being more general in its description, the Official Nintendo Seal does not vouch for quality like the old Official Nintendo Seal of Quality did. The reason for the change has never been officially given by Nintendo, but it is generally assumed that since the extremely low-quality games (sometimes pirated to Nintendo systems) of the 1980s are mainly a thing of the past, Nintendo no longer felt comfortable in labelling all of the games they published as being quality games. Perhaps they also did not want to confuse this seal of quality with the player's choice games, which are popular games that Nintendo guarantees to appeal to most."
http://gaming.wikia.com/wiki/Nintendo_Seal_of_Quality
