WMG / Halloween III: Season of the Witch

The events of the first two Halloween movies actually happened in SOTW's universe.

The Haddonfield murders actually took place in the world of Season of the Witch. The two films that were produced ended up being very loosely based on actual events, thanks to the publicized reports from Myers' old psychiatrist and the traumatized sole survivor - much like Texas Chainsaw's Leatherface is based on Ed Gein.

• Furthermore, 'Michael Myers' or his equivalent in Season of the Witch's world was actually part of a test run for Silver Shamrock's larger plan, using a single mask on an individual to see whether or not trigger signals could be sent to the 'brand marking'. Therefore Cochrane is part of the 'Cult of Thorn' we see in 'Halloween; The Curse of Michael Myers'. The 'Halloween' movie we see in this film is a fictional adaptation for the actual events in Haddonfield in 1978.

SOTW actually does have a connection to the Michael Myers continuity.

It's one of the movies that Annie was watching during her six hour horror-movie binge. We'd have seen its closing credits before the opening title for The Thing came on if the timing of the scenes had been a little different.

For a variety of reasons, the death toll of the children

...was 'only' in the thousands. Some kids stayed out later for more candy; some had families with busted TV's; some were being punished with no TV, and so forth. Needless to say, it was still counted as a horrific event of staggering proportions, yet it was not as bad as it could have been. That said, Cochran was either a pawn of or working for the cult Doctor Loomis faced later in the series. For the sacrifice of the children was enough to resurrect Michael, and make the killer who was previously pain-ignorant and very durable into a true nightmare immortal.

• The death toll would have to include adults. Remember that when we see the 'test run' of the Silver Shamrock masks, it somehow ends up killing the parents of the kid wearing the mask, too; Presumably the death toll could be much higher because events would be made more chaotic by parents being killed as a byproduct.
• Possibly the biggest reason why the death toll wouldn't be particularly high is homemade Halloween costumes still outnumber store-bought ones, and did so to a much greater degree in the decade when this film is set. Most potential targets wouldn't even own one of the booby-trapped masks.
• Let's not forget, a lot of kids probably survived simply because their parents were so sick and tired of hearing that wretched London Bridge jingle that they found some convenient excuse to leave the damn set switched off.

Cochran was Necessarily Evil

As horrifying as the deaths of thousands, if not millions may be, if the sacrifice had not been completed, a much worse catastrophe would have befallen humanity from the wrath of offended deities.

The person who stole part of Stonehenge for Cochran was none other than...

Carmen Sandiego. Search your feelings, you know it to be true. She probably didn't even charge him for it.

The commercial hypnotized or brainwashed children to want the mask over custom or pop culture costumes.

Perhaps it influenced the adults to purchase them as well. "Witchcraft" or "magic" has already been established and the commercial has a lot of patterns in it. It’s not a stretch to imagine there was some kind of mind control so it hits as many kids as possible. Even if it wasn’t through magic, Cochran has access to technology well beyond what was available at the time.

Cochran is an immortal sorcerer.

His way of talking about the ancient Celtic rites is very, very intense, as if he had seen what he tells...

The original anthology idea will be used for a TV adaptation.

Some episodes will involve Michael Myers (directly or indirectly), some will involve a different kind of evil each time. But they all take place during or around Halloween.

How Cochran got Stonehenge to California undetected

So how do you get a chunk of Stonehenge across the Atlantic Ocean and across America without being detected? Cochran had some connections with Omni Consumer Products. He called in some favors "the Old Man" owed him to get that rock.

Halloween was cancelled after the events of this film

The death of numerous children nationwide would likely cause a huge backlash against the Holiday itself, causing Halloween to no longer be celebrated, at least in the United States

Michael actually was in Halloween III.

We just didn't see him because he was manipulating the events off-screen the whole time.

• It's doubtful Michael somehow managed to create a successful Halloween mask company, hire people to run it, steal Stonehenge, build androids, and organise this entire, super-elaborate plan to kill the children of America, all in the span of twelve months.
• It would be a paradoxical if Michael existed in Halloween III as a commercial for "the immortal classic" Halloween (1978) appears in the movie.
• Alternative theory: Silver Shamrock is run by the Cult of Thorn.