Game Version Backwards compatibility

Hello everyone. I have been DMing dungeons and dragons off and on for for over 25 years. This takes me back to the days of THAC0 and the amazing. Cpmbat revolution experienced when 3rd edition came out. I slippes passed 4th edition because like most who commit to the books, they becone irreplaceable. In facr many are. Taking into account that DIfficulty Number concepts have srayed relativley the same ocer the years. Have any of you had any success in using books from the 3rd or 4th era? An example would be the Unearthed Arcana book among several otbrrs thar help enrich my campaigns.

I regularly convert 2nd-Ed material to 5th. Third would be even easier. Haven't tried 4th yet, but I have a few adventures slotted to convert.

It helps to remember to convert the spirit of the content, not the content itself. This may help:
https://media.wizards.com/2015/downl...rsions_1.0.pdf

You are spot in about the spirit of the content. My favorite campaign of all time was the second edition campaign "Council of Wyrm." I still have all of my books and am going to piggyback off the Tyranny of Dragons adventure series. I am almost confortbale enough with fantasy grounds to run a fluid game up to my standards but not quite there yet.

There are lots of old modules with conversion guides already done. You can get more info here; https://classicmodulestoday.com/
And then purchase the conversion guides and the originals in PDF on the https://www.DMSGuild.com

Oh wow thank you very much. I really appreciare these resources

If you use Castles and Crusades all your "old" 2e and AD&D and OD&D stuff converts across 90%+ without needing anything beyond cosmetic adjustments.

If C&C isn't your cup of tea, there's a nice AD&D/2e community ruleset made by celestian I believe.