Lock-down

Question. At what point do you stop creating, and accept that a work is "finished"?

A bit of context: I'm working on a play that is created from about ten different drafts written by the original playwright over forty years ago (and who is, sadly, no longer with us). It's not that different from working on a brand new play, with re-writes happening on a fairly regular basis. This is tricky for the actors (and, in some cases, the production team when key design/atmosphere/costume factors are affected) as entire passages that have already been learnt are suddenly disrupted by the addition or subtraction of a line or two (or, indeed, full speeches).

There are famous incidences of productions running in 'preview' for months before they officially open - using an audience's response to help mold the show until it is locked down. And some plays are such classics you know the script will not change from day one.

Now, the obvious answer to my original question is that you never truly stop creating - that's the magic of live performance, that it is re-created every night and can never be the same. As such I'm not sure it is possible to have a "finished" live performance. But when that live performance relies on the confidence and skill of performers and technicians, at some point you do have to say 'this is it', 'this is what we're going with'. So, when?

Or is the work never done?