Illustrative example. The dates and amounts below are provided for practice.
A birthday observed on March 1 in common years should return to February 29 when that date exists. The common-year rule is a fallback, not a permanent change of birthday.
Set month 2, day 29, Calculate As Of February 28, 2028, and the rule to March 1 in common years. Leave the year blank. The next birthday is February 29, 2028, Tuesday, one day away.
Compare the year before
With the same birthday and rule, use February 28, 2027 as the reference date. The target is March 1, 2027, also one elapsed day away. The equal countdowns conceal different target dates, which is why checking the full date matters.
In both runs, inclusive numbering starting at the reference date would call the target Day 2. Countdown days measure the interval instead.
If a saved calendar continues to show March 1 in 2028, inspect how the event was entered or imported. A manually repeated March 1 event will remain on March 1. Export the original February 29 record with its rule when you need dated future instances.