Does deleting a submission entry reduces the submission space for submission limit?

If I set up a submission limit (without a date limit) on a form, and I delete some submissions, is it the total number of submissions ever submitted, or the current number that counts toward the limit? 

I want no more than 60 individuals to uniquely submit information on my form. Since I opened it, three people have duplicated their submissions, which required me to delete the duplicated submissions. I'm curious if I should expand the limit to 63 (even after I deleted the duplicates), or if it would be okay if I continue to delete duplicates, but leave the limit at 60.

Yes, deleting an entry in your submissions does reduce the count of a form's total submission. For example, if you set the submission limit to 2 and submitted one entry, deleting the first entry would allow you to send another 2 entries (total of 3 entries submitted, while one is deleted).

To prevent duplicate entry, you might want to implement this on your form http://www.jotform.com/help/223-How-to-set-Form-Limits-Based-on-a-Unique-Question.

I hope that helps. Let us know if you have any questions or if you need further assistance.