Based on the wording in the SI and GPS, the penalty points are calculated as follows:
1.8. The “USODA Graded Penalty System” will apply; see SI Addendum 2. “Fleet” is defined as
number of boats entered in the series (see SI 16.2). Percentage penalties will be rounded up to the nearest whole number.
16.2. The number of boats entered in the series will be defined as the number of registered boats which subsequently completed competitor Check-In at the regatta venue. This changes RRS A4.2.
SI Addendum 2 USODA Graded Penalty System – Percentage Penalties rounded up to the next whole number. Penalties apply to the race of infringement; otherwise, to the first race of the day.
I've gone ahead and calculated the points based on the number of boats registered and attached a template. Of course, this may change since I'm not there to see if all competitors complete Check-In at the regatta venue.
Here's what I recommend. At the close of Check-In, the scorer usually gathers all corrections from the Check-In sheets. The scorer will be able to identify if there are any sailors who did not Check-In (in other words, are not attending). Since the PRO will probably already be making his way out on the water, the scorer can adjust the content in the attachment appropriately, print, and post on the Notice Board.