Unity

A Borg mechanical arm was one of the costume pieces that had previously been used in Star Trek: First Contact (1996).

Ex-Borg Riley says she was assimilated at Wolf 359 (re: The Best of Both Worlds: Part 2 (1990)). The Borg ship that battled Federation forces at Wolf 359 later went to Earth and was ultimately destroyed by actions of the Enterprise-D, which would mean that none of the newly-assimilated Borg could have been transported back to the Delta Quadrant. (The fifth season episode Infinite Regress (1998) provides another instance where a character - one of Seven of Nine's personalities - claims to have been assimilated at Wolf 359, thus making the same continuity mistake.)

Edited from Star Trek: The Next Generation (1987)