This discovery, and then removal, of unannounced Microsoft logos is a reminder of something that happens often in competitive intelligence. Articles, quotations, videos or images that have been published online can disappear, removing valuable evidence. Sometimes this is intentional (for example, as with this Microsoft video, if someone has realised that the information should not have been published). Sometimes it is unintentional: websites are closed down or delete pages when reorganising content (as we discussed in this competitive intelligence post, the Wayback Machine can help, but only partially). A similar thing happened recently with a blog relating to Google CEO Eric Schmidt.
The solution is to take local copies of any content that is likely to be removed. Resources allowing, it would be ideal to take local copies of all relevant content, but this can be labour intensive.