Question about LeadFields

General Discussion
1

From https://mautic.org/docs/en/forms/manage_forms.html :

Quote:
Pre-populate the values automatically in an email

Embed the tokens {leadfield=FIELDALIAS|true}, one for each contact specific information you want to pre-populate the form with, into the URL, assigning them to the name of your form field.The |true tells Mautic to URL encode the value so that it works in the browser.

{pagelink=1}&email={leadfield=email|true}
In the rendered email sent to a contact, the URL may be converted into something like:

http://my-mautic.com/my-landing-page?ct=A_REALLY_LONG_STRING&email=contactemail%40gmail.com
So, what happened is {pagelink=1} was converted into the landing page URL and had ?ct=A_REALLY_LONG_STRING appended. The really long string is encoded information about the contact which includes the contact ID. Each {leadfield=FIELDALIAS} was replaced with the contact's data. When the contact clicks the link, they will be taken to the landing page with the embedded form, and the form's 'email' input will be pre-populated with the value passed through the URL.

It appears that in order to populate the proper values for the leadfields, Mautic first needs to accurately identify the contact. My question is: What would make this identification fail? cookies blocked? images blocked? dynamic ip addresses? I'm trying to understand the edge cases for potential errors that need to be handled.
2

From https://mautic.org/docs/en/forms/manage_forms.html :

[quote]Pre-populate the values automatically in an email

Embed the tokens {leadfield=FIELDALIAS|true}, one for each contact specific information you want to pre-populate the form with, into the URL, assigning them to the name of your form field.The |true tells Mautic to URL encode the value so that it works in the browser.

{pagelink=1}&email={leadfield=email|true}
In the rendered email sent to a contact, the URL may be converted into something like:

http://my-mautic.com/my-landing-page?ct=A_REALLY_LONG_STRING&email=contactemail%40gmail.com
So, what happened is {pagelink=1} was converted into the landing page URL and had ?ct=A_REALLY_LONG_STRING appended. The really long string is encoded information about the contact which includes the contact ID. Each {leadfield=FIELDALIAS} was replaced with the contact’s data. When the contact clicks the link, they will be taken to the landing page with the embedded form, and the form’s ‘email’ input will be pre-populated with the value passed through the URL.[/quote]

It appears that in order to populate the proper values for the leadfields, Mautic first needs to accurately identify the contact. My question is: What would make this identification fail? cookies blocked? images blocked? dynamic ip addresses? I’m trying to understand the edge cases for potential errors that need to be handled.