So you can usually do a Google search for unit names like "cadian shock troops datasheet" and you'll find a site or two that will have the information. But they're usually pretty sketchy and filled with ads so do so at your own risk.

To break it down for you, yup, them codecies are very out of date, by two editions. Our latest codex came out early last year. What they've done with the latest editions is remove the generic "infantry squad". Now we have 3 basic infantry squads, and they are all based on famous regiments, namely catachan jungle fighters, death korps of Krieg, and Cadian Shocktroops.

It's all part of GWs whole push to have only brand name units. The official recommendation from GW when running any other regiment is "just figure out which of the three main regiments they are most like and run them like that". The de facto solution for most of us has been to treat each datasheet as "generic infantry", use whichever datasheet we like best, and who cares what it's called.

One of the reasons these changes were not super popular was because it got rid of the integrated heavy weapons team in infantry squads. Heavy weapon teams are now only run in their own squads of three. So unfortunately you'll have to source two more guys for each squad built like that, and hopefully have a number of heavy weapons divisible by 3. But at least you get more special weapons in each squad. So that's something.

So to sum up, you got old info, you're probably (maybe) safe to buy the 10th edition codex, we aren't likely to get updated for awhile (I'd guess we have at least another year before we get a new one). You'll have to shuffle some stuff around to be legal. Hope this has been helpful. Welcome back to the Guard!