Absolutely brilliant news, well done!
Now, as you said, the adolescent months are coming. I had a great recall on whistle at six months and I completely poisoned it through my own stupidity. If Harry one day doesn’t come to the whistle the first time because he’s distracted DON’T BLOW IT AGAIN. Wait for him to come back then do some reinforcing whistles close by with few distractions. If he starts wandering further than you would like, nip it in the bud IMMEDIATELY. For dogs, being allowed to do something one time means they can do it any time. Cockers are champion at taking an inch, then another inch, then another, until they are a mile away and wonder what you are jumping up and down about.
If you remember to keep your recall honed over the next few months, and don’t make the mistakes I made (blowing the whistle again and again, teaching him that ignoring it was okay, letting him free hunt, disappearing into the woods etc), then you’ll have a fabulous recall forever. You’ve done all the hard work and laid down fabulous habits. Keep going!