When adding repeating appointments with an end date of "Never" you'll notice on the right hand side that "Never" doesn't bring up dates from today through eternity. Instead we use your advance service booking or advance class booking settings to determine how far out to add repeating appointments and then continuously add them as your advance booking date changes.
To illustrate how this works, let's say you are adding a repeating appointment for the service "Consult" starting today with the end date set for "Never":
You'll see that the preview on the right only shows appointments until January 13th, 2016:
This is because the service "Consult" on this account has an advance appointment setting of 3 months:
Thus in initially creating the repeating appointment series we only extend the series out as far as people are able to book. This helps to speed up save times.
You'll notice if you check back on any appointments that are within a repeating appointment series that you've created (a few days or a week after creating them) that new appointments will be added once the advance appointment date approaches.
So if your advanced appointments is 30 days and you add a repeating appointment starting Monday October 10th, repeating every Monday with a "Never" end date, then at first the dates on your right hand side would just be October 10th, October 17th, October 24th, October 31st, and November 7th (since 30 days from October 10th is November 9th). Once October 15th rolls around, however, then 30 days in the future is a new Monday: November 14th. Since a new Monday is on the horizon, our repeating appointment extender tool will automatically add that to the series.