“what about the games which were developed after Sierra’s demise, but by an
acquired studio (for example the citybuilding series by Impressions, the Tribes
series by Dynamix or the later Nascar titles by Papyrus”
If it were up to me, I would include the games developed by the traditional Sierra family company that were still developing games after the closure of Oakhurst. Even the 3-D Ultra games are a continuation of the physics that Dynamix developed. I would not include any of the games that were developed by companies that no association with Sierra before the demise.