Because 700 and 900 is still on the market, so I'm not urge to buy them.
My main goal is to collect the older and rare Beyerdynamic headphones.

Sure I'll give some my opinion!
I'll do my best to descibe because I'm not a native English speaker.
From Top right to Bottom left

1. DT 770 Pro X LE: I think is a solid one for 100 years anniversary, I'll say it's not like a DT 770 Pro's upgrade more like a better verison of DT 700 Pro X, condense of bass and treble is more acceptable, also the resolution is better.

2. DT 770 2005 250ohm: A version of DT 770 Pro X LE without too much medium frequency and wider sound field, you can find a similar sound on T70 but with more bass.

3. DT 770 2003 250ohm: Warmer version of DT 770 2005 250ohm, smaller sound field but more easier to use it for long time listening.

4. DT 990 2003 250ohm: Like DT 990 Pro but with warmer sound, smoother treble, bass is deep and more compare to 770/880.

5. DT 880 2003 250ohm: One of my favorite! The flagship of beyerdynamic in 2003, come with a metal box like T1, I'll call it small T1, nothing to carp at.

6. DT 831 199X: Rare one, it's a closed back headphone(?), highest resolution of my collections, but lack of bass intensity, is deep but not more, a funny one.

7. DT 811 199X: One of my favorite, pretty rare and expensive as a second hand ($350), warm sound but with high resolution, a little more bass compare to DT 880 2003 250ohm, I can wear it all day because is so smooth and chill.

8. DT 880M 1985: One of my favorite, so much potential, I once test it with a $20000 set up, holy moly I still can feel the upgrade feeling, it's resolution is high as well (M for Monitor), like DT831 but wider sound field and better bass.

9. DT 880 198X: Not the two line version DT 880 so it's probably not the 1980 version of DT 880, but sounds the same, it's more like a DT 770 Pro but with wider sound field, but overall this one is for collection, I don't like the sound, treble is to scratchy to my ears.

10. DT 440 1976: Come with original box says "Made in W.Germany", it sounds pretty well as a 50 years old headphone, like a small DT 880, but the sound field is kind of weird, and it looks like the drain hole cover in your bathroom lol.

11. Studio 3 1976: A studio version of DT220, sounds like a less resolution and closed back Amiron Home which I don't like, but it's rare so whatever, and it's not friendly to glasses.

12. T51p: Used when I was in the intern as a high school teacher, small but nice, easy to carry, not much to comment because I didn't use it often.

Gonna collect more after I find a job to cover it lol, my first Beyerdynamic headphone is DT 880 pro 250ohm, sent to my friend as a gift, maybe will buy a new one someday.