At what point in the building process is the can done ?

Is it after its built as you originally planned ? 
what if after 2-3 test shots you decide it needs another baffle or a different length spacer for the blast chamber?
is test firing a suppressor "finishing" it or is it part of the build procedure? 
what if the baffles need to be clipped ?

I'm not talking about repairs or replacing worn out parts

I know that a F1 isn't a permission slip to "experiment", however where is the line between work in progress and a finished suppressor?

ETA: FOR THE LOVE OF ALL THINGS DO NOT WRITE THE ATF AND ASK FOR CLARIFICATION 

When the ATF kicks in your door and shoots your dog.

I kid. I imagine, it is when it was built to the specifications as listed in your Form 1. I think this is why you used to have to submit drawings.

I've never had to submit drawings just an OAL and cal.
That leaves a lot of room for interpretation   

It is complete when it is complete.

If you are flirting with the legalities of modifying a silencer after completion, think of it in a risk/reward type scenario.

For most the risk is not worth the reward.

Some things like clipping baffles is always ok, other things like adding a baffle are not.

Every situation is different, but IMHO $200 and trying again is the cheapest option.

I'm not talking about modifying it after its "Finished"  and you come back 6 months later and want to add a baffle but rather the following examples

All of the following are purely hypothetical

Say its built and not fired ,you then decide its not finished and would like to install another baffle. Is that OK or is it breaking a rule since its been fully assembled?

Now a little more gray area lets say I'm in the garage making my suppressor on the lathe and wonder if it will be good enough with 6 baffles or do I need 8 (I'm trying to keep it light) so I assemble it with 6 baffles then proceed out to my backyard range and test fire it then decide it really does need those other 2 baffles so you go back in the garage shorten the skirts on the current baffles and make 2 new ones. ?  have any rules been broken ?

What I guess I'm asking is what defines completion ?

Ive stuck to the premise that once you've put a round through it, no more meddling with the overall design. Clipping, porting, baffle config/orientation, removing material, etc, all ok. No adding or swapping parts.
     
There's no difference between a can w/ a single round count, to one that has 10k and needs a recore. If you test fire your can and decide you need another baffle, in my eyes, you're operating at 02/07 level. The same as that 10k can that needs new baffles.
     
Learn from your mistakes and put that knowledge into the next build. It's only $200 and some metal. Not worth the legal troubles. Not that you're ever likely to get caught, but same same.

   And never, ever, under any circumstances should you post about any grey area shit you've done or start writing letters to the ATF for "what-if" scenarios. No one's going to win, especially not you.

Only ATF can determine that, you won't know until you are charged.

Considering the general public still thinks silencers are illegal to own, what are the chances 12 people will rule in your favor if ATF decides what you did is illegal.

ATF has historically had the opinion that everything grey is illegal. It takes court rulings to keep their opinions in check.

ATF has never inspected any of my form 1 cans. you aren't required to tell them when youre finished, so how will anyone ever know? I could theoretically destroy one of my form 1 cans and rebuild it. Short of posting it online and telling everyone or writing the ATF, no one would ever know. Theoretically, of course.

when all the nessassary parts to build ?xyz are together at the same physical location at the same time.
Assembled or not ! Unless you are a licensed manufacturer.

Since that is what would get you arrested if you didn't have a form 1, thats probably the best answer of the thread.  It also means don't buy all your parts until you have a stamp in hand, I wouldn't want a pending F1 to be my defense in court.