My Two Elelphant hearts are still in the fridge. Out of sight, out of mind 
I picked a few Euro plums today. I go by what the tags say (quite a few mislabeled I’ve found out).
Top row from left to right:
Coe’s Golden Drop. Big disappointment this year. 50% of them dropped prematurely with no reason. The ones that looked ripe were not sweet and rather dry. Could not squeeze juice out. No brix reading.
Vision- very large and great tasting. Sweet with a bit of tang. Brix 21.
Bottom row:
Middleburg (could be Imperial Espineuse - rather bland, firmer flesh and not juicy enough to get brix.
Unknown (French Improved?). Very sweet, soft texture. Excellent. Brix 26.
Castleton - I let mine become very ripe and soft. Brix 24. The ones that I picked when firmer were not as sweet.
@scottfsmith - could you please let me know whether or not my Middleburg is correct and the unknown is French Improved?
Several Middleburg have not ripened yet.
The Unknown are small to medium, reddish color. Ripening time started a few days ago. Excellent taste.