Dragon was my first ever magazine subscription back in the day. I think I started with issue 55 or so, but it may have been 58. I had bought a few issues at my FLGS before I begged my parents for a subscription and 58 on are the covers I most definitely recall. Anyway I loved Dragon magazine beyond it simply being my first subscription. More so than my comic books when I started collecting them. I'd give my eye teeth to get both of my collections back, Dragons and my comics. At any rate, I have been meaning to rebuild my collection for some time now. At least the issues that interest me. Which got me to thinking as I was compiling my list of AD&D resources. When exactly did Dragon become 2e-ified? So a quick poke or two round the net turned up the following.
First we know that 2e was released in the late summer/fall of 1989. So checking the issues in '89 we get the following. By issue 142, February of '89 the official 2e preview is included as a lengthy insert. This s the first "taste of what the upcoming revision is going to be like, but the magazine is still predominantly catering to first edition rules. Then in issue 147, July of 1989 articles are turning up that are influenced by 2e or are covering content aimed at 2e. By issue 148, August 1989 regular columns, like Sage Advice, officially get switched to a 2e focus, Though there are still switched back and forth, I'm assuming to use material previously written.
Which brings up the point that much of what was produced for 2e in the magazine also applied to 1e and vice versa. So though by issue 152 in December the focus predominantly shifted to second edition there was often a generic focus to articles that could apply to either edition. Though when rules are quoted 2e generally becomes the default. This approach was largely taken because of the claim made in the preview mentioned above that 2e was not designed to replace 1e that much could be used interchangeably. While in theory this was true the system took the shift to 2e by 1990 wholesale.
So in looking towards resource for Advanced Dungeons & Dragons I would recommend everything before issue 152 without reserve. But truthfully, one could find benefit in most of the issues after 152 up to the time WoTC took over. This would have been around issue 237. By this time WoTC is at the helm and this issue is a poor mish mash of stuff showing the lack of direction in a time of transition. After this time WoTC shifts the mags focus to proprietary products only and the build up to 3e.