I think it goes by your IP address and email. And probably in the Turbo Tax program. 5 efiles is an IRS limit. It's to prevent fraud and people filing fake returns. To do more you have to sign up as a ERO - Electronic Returns Originator and be an authorized E-file provider. https://www.irs.gov/e-file-providers/become-an-authorized-e-file-provider. To do more than 5efiles you have to buy Intuit Products for Tax Professionals at https://proconnect.intuit.com
This post has info explaining 5 efiles
https://ttlc.intuit.com/community/taxes/discussion/re-re-e-file-limits/01/2471668#M883293
