Character mistake: When the now human Borg children are sculpting, one of the children tell Seven he made a cube that's precisely 1/1,000 the size of a Borg vessel. Borg Cubes are described as 3 kilometers in length, if not bigger. 1/1,000 of that would be more than 9.8 feet in length. 1/10,000 the size would have been a more accurate description.
The Haunting of Deck Twelve - S6-E25
Character mistake: When Chakotay states they have collected 80% of deuterium and he suggests to stop taking in more, Captain Janeway agrees and she then tells B'Lana that they will stop taking in dilithium. (00:09:50)
Character mistake: B'Elanna replicates and assembles a television from 1956, including a remote control. Tom however says they didn't have remote controls in the 50's. The first wireless remote was invented in 1955 and the "Zenith Space Command" (a remote looking similar to the one in use) came out in 1956, which fits the timeline. Tom is vastly aware of 1950's technology (he seems to know when the television remote came out) and wouldn't make that mistake or B'Elanna would have corrected him given how much research she had to do to set the whole thing up.
Chosen answer: Before Q sent the Enterprise to the beta quadrant to officially contact the Borg, there were already indications that the Borg was beginning to reach Federation territory. There were remarks towards the end of the first season of the Next Generation that several of the furthest Federation outposts were being attacked by some unknown enemy. They suspected the Romulans, but when contact with the Romulans was re-established, they learned that it was not them. The Hansens had simply figured things out much earlier than anyone else in the Federation. They learned about the Borg nine years earlier, but Starfleet mainly took notice when their outposts started getting wiped out. It is logical to assume that there were indications of Borg scouting parties and research efforts well before that.
Garlonuss ★