What does this text in the first paragraph mean?

If recurrence for the Missing E-mail or Profile Data validation is set to 'Once' users in these Roles will only be shown the validation message one time, unless the recurrence frequency is later changed to a shorter cycle.

If you choose "Once", users will see the validation only 1x and that's it. They will never be prompted to change it again. So, the "shorter cycle" text refers to length of time the setting is effective. "Once" is effective indefinitely. However, the other settings (30, 60, 90, etc.) have a specific number of days they are effective. So, they’re considered a “shorter cycle”. If you want users to see the validation message again, set it for one of the shorter (30, 60, 90 day, etc.) cycles.

What does this text in the second paragraph mean?

Additionally, Missing E-mail and Profile Data validations cannot be 'reset' for a Role by changing the recurrence setting to Off and clicking Save or by selecting the Remove checkbox and clicking Save.

Once a user validates their profile, it depends on what the setting was at the time a user validated their profile. This is best explained via an example.

With the validation set to 365 days, User1 logs in, is prompted to change their information and they change it. Then the validation is changed to 180 days. At this point, User2 logs in, is prompted to change their information, and they change it.

User1 will not be prompted to change their information for another 365 days from the date they validated it, even though you have since changed the validation frequency to 180 days.

User2 will be prompted to change their information 180 days from the date they validated their information.

The only way to change User1's validation frequency to 180 days, is via a data fix. In this instance, contact the Support department for assistance.