I am guessing you are talking for new submissions... since you can already see what you submit on updates. And that does sound like a good idea. I would add something to this though... I would also like to choose how much of the new submission to contribute... have check boxes for new submissions just like we have for updates.

I am confused. Isn't the page where you have the Submit and Cancel button the preview page?
There you can already see if BY are added or not. All birth years not already in the main database have to be checked at the end of the preview page. All other additional birth years appearing in the cast and crew list are propagating birth years. When in doubt I always remove those locally and resubmit without the birth years.

I look at the current contribution page as more of a Comparison Page.

Yes the current Comparison page shows All the Birthyears, even those that I want to keep local only. And that's the problem. Let's say a profile has 4 needed BYs that I;m aware of. Let's say that 2 accepted BY's that I wasn't aware of is also included. Now let's say that I have a total of 50 BY's in that profile. I have to look through 50 highlighted names one by one to make sure that either my local BY's don't get contributed by accident or that some BY that shouldn't be in the database but is approved before is also included.

By having a Preview option I could see what BY's would actually be included in my contribution and not be contributing local only BY's, error BY's or un-needed BY's.

But perhaps my entier suggestion is just stupid or I'm not wording it right or voicing my concerns more clearly.

If that's the case then just ignore my suggestion. But I can't see what the hurt would be to have a Preview Contribution option.

Maybe a local preview button, before actually contribution, would be nice. As said, now you have to contribute, and cancel if you detect a mistake.