In theory, your plan will adapt up to the day prior to your B and C races (by assigning some openers), so you can add B and C races as you go, and Plan Builder will offer the option to recalculate!
You’ll just want to keep in mind the practical time frame depending on the priority event (e.g. A events will have a taper week/opener workout, B events will have opener workout/remove the workout the day before/after the event, C events will replace the workout for that day with the event).
Fingers crossed we get to add plenty of A, B, and C races to our calendars soon! I know we’re all going stir crazy! 
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