Here are some photos of the crowding. Any suggestions? Also, I found my notes. It is an Iceberg.
{{gwi:644467}}

{{gwi:644469}}

{{gwi:644471}}

Here's one that escaped crowding
{{gwi:644472}}

And my Swan's Olympic Flame opened, too. Yippee!
{{gwi:644474}}

I have both Iceberg and Snowbound this year, but neither are near budding yet. Iceberg is supposed to have pinkish tips to its pettles, so I'm guessing what you have open there is Snowbound. Iceberg is 12" diameter, Snowbound 9". Iceberg is 36" tall, Snowbound is 48".

Short stems can be a problem. I had that problem last year with my Purple Taiheijo (which is sister to Iceberg btw.)

You can disbranch, or if you have buds above the blooming flowers (which you appear to) simply go ahead and remove the bloomed flowers for your vase.

It can take a week or more for a bloom to fully open, especially the AAs. I recently had a 4" bloom that took >2 weeks to open fully.

I don't have a lot of cutting experience for vases, but I cut them when they look nice...who cares if that's 50% open or 100%.

Mine did not continue to open after I cut them. YMMV.

Congrats on growing such beautiful Dahlias!

Cheers,
Russ

Here is a link that might be useful: Learning: Controlling Plant Growth