It is already longtime no surprise anymore for me how sometimes very strong players prepare their games very poorly. It is really not only amateurs as described in my article password whom don't optimally prepare. Previous article is a model example of how one should not prepare. You are an international master and you play a closed grandmaster-norm-tournament in Czech. The pairings are known well in advance and you only have to play one game each day. Still you manage to miss an important game of your opponent played over 1 year ago. Although this game was inserted in any commercial database.
Funny or rather sad is a Chessbase article published a few months earlier. In this article the British grandmaster Daniel Gormally explains how he despite preparing well with chessprograms (databases and engines), lost against a 300 points lower rated opponent. However his preparation didn't take into account one very important element. His opponent was a very experienced and strong correspondence-chess-player: the British Senior International Master John Anderson.
Now it is clear that Daniels opening-choice wasn't very smart. Choosing a sharp opening as the stronger player is already risky (see my article how to win from a stronger player). If you combine this against a player with loads of correspondence-chess experience then all ingredients are there for a very nasty surprise.
Daniel did't have the chance to play before a correspondence-game against John will surely be an excuse some readers will use to defend Daniel. I don't accept such excuse. In my article using databases I explain how to use the correspondence-database to extract the optimal moves in a variation but that is not the only reason why to use that database. In my preparation I will often check if my opponent doesn't play correspondence-chess. By doing so I found out that not only former world champion correspondence Gert-Jan Timmerman playing for KOSK, but also Rene Beniest plays correspondence-chess which could've played an important role in the interclubmatch against SK Oude God.
Solely looking to the correspondence-database to define if somebody is an (active) correspondence-player isn't fully safe. I played 20 correspondence-games in my career and only 1 fragment of a game can be found in the database so I can imagine many correspondence-players are not even mentioned. Therefore it is not redundant to check some sites like ICCF, IECC, FICGS in which I encountered the for me unfamiliar Belgian topplayer Jeroen Van Assche recently made the transfer to ICCF. This transfer is no surprise as ICCF is the place to be in correspondence-chess.
I also want to honor our Belgian correspondence-federation still each month publishing a free open and nice magazine of which we can only dream about in standard chess especially after the recent general annual meeting. Scrolling through the current list of correspondence-members I remark our Belgian topplayer Francois Godart. Maybe he joined after being inspired by our Dutch neighbors where several strong youth-players started with correspondence-chess: Etienne Goudriaan, Twan Burg. In any case I believe that a few years correspondence-chess can be useful for standard-chess as you learn how to work properly with databases and engines which after reading above article surely can't be considered anymore as a luxury.