FYI - the forum isn't really officially open to the public yet. They are still developing and testing the new forum software. So this thread, and others, that were created before the forum is 'open' are subject to being deleted as part of the cleanup done for opening the forum.

During any daily editing session on my Montage M7 I may make many changes to my user performances. These create multiple copies of the same performance with what appears (in Category search) to be the same name.

Correct - if you choose to 'Save as New Performance' but use the same name then you will have multiple performances with that same name.

If you don't want to create a new performance after making changes choose 'Overwrite Existing Performance'.

Looking at these via the Data utility page doesn't reveal any way to distinguish which ones can safely be deleted as there's no visible time stamp.

As far as I know that is correct - on that page they could be listed in any particular order.

The Category Search screen has an option to sort by 'Date' - which is curious since, as you mentioned, you can't actually provide or even see a date.

Use sort by data and then choose the LAST one listed and rename it. Then you can delete the others that had the original name on the Utility screen.

Are the older copies automatically deleted and if so what is the criteria for when that happens?

No - the performance will be saved using whatever name you provided. For whatever reason Yamaha doesn't prevent you from creating as many copies as you like with the same name.

Thanks.

Regarding the forum being "open", as far as I'm concerned, if I'm allowed to log in, read and post messages, then I'd have to say it's indeed "open" despite the "Under Construction" message.

I've never seen a message forum that's been both publically available and accepting new posts being somehow considered not ready for use. It's either available or not. If not, then it should be kept offline or otherwise prohibiting logins. This forum upgrade situation has been and continues to be a confusing mess for the user community (at least the ones I've talked to on other forums). And it hasn't helped that Yamaha hasn't offered anything by way of explanation for why this situation occurred and most importantly an ETA for full availability. 

I've never seen a message forum that's been both publically available and accepting new posts being somehow considered not ready for use.

Right there with you. I could care less if you, or anyone else posts. I was just giving you an FYI that:

1. it isn't 'officially' open

2. some functionality doesn't work at all and other doesn't work the way it should

3. threads posted after it closed and before it officially reopens are subject to being 'cleansed' as part of the reopening

It's either available or not.

Sort of - subject to what I just said above - you use it at your own risk

If not, then it should be kept offline or otherwise prohibiting logins.

Yes but 'should be' are the operative words. The login capabililty and been enabled/disabled several times in the last couple of months. If you aren't logged in and hit reply to login is typically didn't work. But if you clicked on the profile icon at the top and logged in then it did.

At one point they exposed the profile info (email, etc) of ALL members if you clicke on the 'Member' icon even if you weren't logged in.

The Yamaha dev team is using this very site/page for testing so things come and go without notice.

Just letting you, and others know, so they are aware they are unlikely to get any responses to any threads they create except from me trying to let them know the status.