I had two <tier 6 horses as of the 03/20 update. One was correctly converted to a tier 6, the other (good ole "Disposable") is just... missing. Not in a stable. No map marker.

My t4s and t5s were changed to t6s, as was communicated.

My t1s were removed.

Not what the patch said.  Not what the loading screen says.  Not what the announcement said.  I was ready to imperial trade those, then was assured by the announcement that t1 to t5 mounts were not being deleted, with no qualification of that statement.

There was also no indication of the action that you said was taken.  No mail, no accounting.  

Little impact in my case, but on principal: this whole series of events was shady at best.  Don't "explain". Don't excuse. Do better.  (do not "improve")

Like my compatriot above noted, that isn't what the patch notes nor the loading screen said, nor for that matter was that implied in the announcement of the decision. There was a communication breakdown somewhere. While I am glad that not all the mounts were trashed, it is definitely tempered a bit that some still were, especially after it was communicated that it wasn’t going to happen.