In the English Grammar Profile, C1 point 205 in MODALITY is defined as:
PAST, NEGATIVE: ‘needn’t have’ + ‘-ed
It means that somebody did something, but it was not necessary. Also, note that uncontracted ‘not’ is possible.
Here are two examples:
You needn’t have come so far, Asgardian.
In fact, she need not have hurried.
Well, we needn’t have worried.
A search in iWeb:
need n't have _VVN
1 NEEDN’T HAVE WORRIED 895
2 NEEDN’T HAVE BOTHERED 117
3 NEEDN’T HAVE FEARED 15
4 NEEDN’T HAVE HAPPENED 11
5 NEEDN’T HAVE LOOKED 9
6 NEEDN’T HAVE FRETTED 9
7 NEEDN’T HAVE DIED 7
8 NEEDN’T HAVE TAKEN 7
9 NEEDN’T HAVE SPENT 6
10 NEEDN’T HAVE GONE 6
*we can see this is a very rare structure.