I’ve investigated database issues before but it’s worth revisiting this subject. There’s really way too much information out there and then it’s often filled with mistakes. What improvers really need is just enough to engage the mind so that it can grasp the method being employed.
Here’s a game by Lajos Portisch from the days when he played the Closed Sicilian as White, an opening that he would later recommend in the brilliant How to Open a Chess Game, a book which he co-authored with some other illustrious players. At both Chessgames.com and in Megabase 2013 there are horrible errors in the notation, which means that it doesn’t make sense. This is quite a loss as it’s a beautiful illustration of how to play this type of game, so here’s my ‘interpreted’ version: