Is your pup from working lines or show lines? WL long coats tend to have shorter coats than SL long coats, although still significantly floofy when compared to standard coats in either line.
I'll share Baron's (WGSL) transition like the other's above have to give you more material. His adult coat really started to come through 7-10 months.
8 weeks old (the day we brought the fluff ball home)
7months (quite a change in just one month!)
Now at 16 months (sloppy stack