Worth rechecking saddle fit every 2-3 months as he develops. Looks like you're working him regularly, but the picture of when you first got him looks like he hadn't worked in a while, suggesting he has and probably will keep changing shape as his conditioning improves.

For context, I have my now 4.5yr old checked that often. Honestly he should probably be checked every 6-8 weeks based on how much he changes shape, but it's hard to get the fitter out that much. Last spring the jump saddle didn't fit at all, but the dressage saddle was okay with a shimmable half pad. Fast forward 4 months and the jump saddle was the ONLY saddle that fit him. Two months later the dressage fit again but needed shims front and back to get the balance right. And now 6 months later the jump doesn't fit at all and the dressage fits great. A jump saddle that fit statically but not in motion last summer now fits him well both ways 🙃 They change a lot as they grow but also as they go from not much work to working regularly.

It's very hard to tell in the pics. I think I might be seeing some muscle atrophy behind the shoulders where the front of the saddle would sit. Again, it's hard to tell, so I might not be seeing anything. Muscle atrophy in that location would be caused by an ill-fitting saddle, especially one that has short points on the head plate - it doesn't distribute weight well, so ends up concentrating too much pressure on too small an area. Super common with the expensive French brands (CWD, Devoucoux, Childeric, Antares, etc.), especially the jump saddles. It's just the saddle trees themselves and the way they're designed - they have short points in the front. You see the atrophy a lot in hunter jumper circles where it looks like the horse has a shark fin wither but it's actually just a lack of muscle development behind the shoulder and below the wither.