During Almost Like Being in Love Tommy picks some flowers, then drops them on the path. Between shots they disappear.
At the end of "Heather on the Hill", Fiona Campbell drops some heather on the ground when she runs off. When Tommy Albright follows a few seconds later, the bunch of heather has disappeared.
The date of the wedding is recorded in the family Bible as March 24, 1754. Fiona later states that it is a Friday. March 24, 1754 was a Sunday.
The villagers seem in awe of the visitors being from America. One even says, "Oh, you're an AMERICAN?" However, in 1757, the United States was not yet an independent nation and its residents were still subjects of the English King George. The title of "American" was not in common usage until the Revolutionary War (1775), so it's highly unlikely that anyone in a small isolated village in the Scottish Highlands would use it. Even if someone did use the term, there was nothing about being American that would inspire amazement.
The lass who calls Jeff a "Winnin' lad" then kisses him, complains about the lack of single men in the village.
The later wedding scene shows this claim to be ridiculous. Men far outnumber women in the wedding scene, and most are strapping young lads.
The only possible counter-argument is that they are mostly married, but this would require them to have left their wives at home.
This, also, would be ridiculous, as no woman would willingly stay at home for a wedding in a small village.
As Mr. Lundie tells the story of Brigadoon, in every reference it happened long ago. He always says 'was' instead of 'is' even though the enchantment only happened less than two days ago by his reckoning, and thus is still in his present time.
In response to the first Anachronism re: date of 1754. In the original play, it was 1747, as the play opened on Broadway March 13, 1947. The law prohibiting the tartans, kilts, bagpipes and arms went into effect in late 1746/early 1747. Tartan trews and kilts would have still been worn. As an aside, Roman Catholicism was practiced by many clans, and Protestantism was practiced by other clans. Catholic & Scottish Episcopalian clans tended to be supporters of the Jacobites (losers of the battle/war) and Protestants were supporters of the Hanoverians. The Campbells (the family name in the play) were supporters of the Hanoverians, delaying their proscription of wearing Highland clothing.
The events of the movie are said to take place (essentially) in 1754. The '45, the rebellion in which Bonnie Prince Charlie unsuccessfully led the Highlanders against the British, would have occurred 9 years prior to the "miracle" being placed upon the town. The disaster at Culloden which ended the rising occurred in 1746, and immediately after the kilt and tartan were forbidden to be worn in the Highlands. Therefore, it is highly implausible that as much tartan as is visible in the town would have been located over the course of two days after being proscribed for eight years. Additionally, the colors of the tartan are far too vibrant for the time.
When talking to Mr. Lundie, Tommy says that they are from New York, which was renamed from New Amsterdam, after Mr. Lundie seems not to understand the location. New Amsterdam was renamed New York in 1664, 90 years prior to the events of the film. This would have been common knowledge, making Tommy's explanation unnecessary, as well as Mr. Lundie's reaction ridiculous.
In the 18th century, the Scottish Highlands were by and large Catholic. It is therefore implied that the entire town is Protestant in the discussions of Mr. Forsythe as a minister, rather than a Father Forsythe as a priest. This would have been highly unlikely in 1754.
During the wedding procession the drummers' actions do not match the cadence.
During the song, "Almost Like Being In Love" Gene Kelly dances around. When he passes the bulls, you can see the bushes to the right of the pig moving as if someone off screen is putting them back in place after moving them out of their way.
In response to the Crew/equipment visible during "Almost Like Being In Love" The bushes seen moving next to the pig as Gene Kelly dances by are almost certainly moved into place to cover camera dolly tracks. The camera angles seen during that part of the dance number would have taken the camera right through that area of the set. To guarantee no vibrations are transmitted to the camera, camera dollies run on light tracks that can quickly put down and taken back up for different angles and or different scenes.
If Minister Forsythe made the miracle happen from outside the village and was not part of it, only two days prior to the villager's time line, and they could not leave the village, they would have no way of knowing it had actually happened. The minister could merely be missing for a couple days for all they knew. In fact, the minister's missing presence conveniently allows the story to develop angles that can't be explained, such as why he felt he had to leave his beloved flock (his advancing age is given as a reason, but that makes no sense, a devoted minister would never leave his flock), why he had to say his prayer from outside the affected area instead of remaining with them, or why they only wake up every 100 years instead of just becoming invisible to the world and continuing to live life as normal, or any number of plot points that don't make sense when tossed together.
For only being enchanted for a period of less than two days (the day of the movie being only their second day awake since the enchantment), by their own time line, the villagers have developed a rather implausibly complex set of customs and beliefs related to their enchantment.
The inhabitants of Brigadoon would have no way of knowing that a single person leaving the village would make them all disappear forever. It's highly illogical to believe that was part of the prayer that enchanted them, especially as that was not related by Mr. Lundie in his description of events. In fact, it's a very implausible part of the story, though it does add to the story line. One renegade could ruin it forever for the whole village, negating the entire miracle. And in a village of that apparent size (many dozens of people partaking in events), it's inevitable that someone would want to leave, as happened less than two days after the miracle, dooming the entire village instead of saving it. In fact, the 'leaving' rule runs contrary to the nature of the miracle, which is to save the entire village from outside influences, not inevitably doom it because of one foolish person.