She barely made it past the new moon. Dipped about 8 times during
new moon, and ended up with a cursed thoroughly rusty corroded
long sword. Was dipping again at the oracle fountains and a water
demon summoned Yeenoghu. 3 teleport scrolls in my inv, but those
don't help against those guys.
Playing during the three or four day period classified by
the game as a full moon positively affects in-game Luck.
Playing on Friday the 13th negatively affects in-game Luck.
Playing during the three or four day period classified as a
new moon has no effect on in-game Luck.
All three external 'events' are based on when you started
the current play session. If you save and restore they will
be rechecked. If you start before a date-based event and
continue play into it, it won't be rechecked and won't matter.
If you start during an event and continue after it would have
expired, that also won't be rechecked and won't expire in the
game until save and restore.
The game also has nighttime and midnight-to-1AM 'events'.
Those are rechecked dynamically as you play whenever a
situation where they matter occurs. However, they are
based on the computer's idea of local time which might
differ from actual local time depending upon how the
computer's clock is set or upon location of a remote server
when applicable. Nighttime isn't seasonal; it's an arbitrary
period starting at 10PM (inclusive) and ending by 6AM
(exclusive; in other words, 5:59:59.99).
[End of new moon vs Excalibur digression....]
In-game Luck is not a factor in converting a long sword into
Excalibur anyway. You need to be at least experience level 5
and pass a 1-in-6 chance (completely random, not biased by
in-game Luck). If you pass that, you also need to be lawful.
If you dip a long sword when your level is too low or if you
fail the 1-in-6 chance or if Excalibur already exists, you will
get the water damage effect.
Failing a 1-in-6 chance 8 times is unlikely but not impossible.
Another possibility is that Excalibur was in a bones level you
loaded (maybe without being aware) so already existed.