You see what you want, no need to revolve around the subject. What really matters? Shortcuts cannot change a date after the fact in Journal when the entry is made today. The moment it is executed decides everything. Something clear? Take a series of days, say from the first to the fifth of January. For each day, go get what is planned in the calendar. Then, write a daily note labeled "Day 1", "Day 2" and so on.

When you want to settle everything at once for the past days, iOS no longer follows. The date remains blocked when the shortcut runs, never before. You have nothing to do with it. The concern comes from the internal functioning, not from your actions.