How to properly limit a web form

I've got a web form that I was to place a restriction of 25 submissions. However there are a few submissions already there and I want to make sure those won't count against the limit but only new submissions. 

Currently I have it set to 40 submissions so we can do testing. But once we're ready to go live, I'm going to want to make sure only the first 25 people to order actually get through and no one else.

Also, once that limit is met, is there a way to reset it so I can limit the submissions again? We're wanting to keep it limited each month while we test out our product before an unlimited release later on.

I know where to go to set the limit, but I just don't know how it actually works behind the scenes. Can you give me some guidance?

Please refer also to the user guide -How-to-Limit-Submissions-in-a-Form

From what I understand on your description, you will be using the limits using the number of Submission Limit

Currently I have it set to 40 submissions so we can do testing. But once we're ready to go live, I'm going to want to make sure only the first 25 people to order actually get through and no one else

How about if you just start the form with clean slate of submission?

You can do this by cloning the form. The new version of the form will then have a clean slate(0 submission)

user guide: -How-to-clone-an-existing-form-from-your-account

On the cloned version of the form, you can set the Submission Limit to 25.

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Also, once that limit is met, is there a way to reset it so I can limit the submissions again? 

Once the form that have a Submission Limit set reaches the limit (in this case 25) it will stop accepting submission.

You will then have to set a higher limit if you want to have it another set of limit up to that the same number (i.e 25, 50, 75...)

OR

Just create a clean slate again by clearing the existing (25) submissions.. you can backup first the data before removing them on the form. You can backup by downloading the submission data

user guide: -How-to-Download-Form-Submissions-as-Excel-CSV-PDF

After clearing existing submission, set again Submission Limit to 25..

If OK with you, you can also repeat the process of cloning form to have new starting form. But this will make you have multiple forms (there is no limit as up to how many forms you can have on your account.. so this is OK also.)

Hope this help. Let us know if you need further assistance.

Thanks.