Some would say I've been researching Vampires all my life because as a kid I would read any book I could get my hands on, learning about different rules and beliefs from around the world regarding Vampires, which rules apply to which fictional portrayals, and possible origins of the belief in Vampires. Obviously if you're making a fan film of a particular property, you want to focus your research to the lore established in that. But you also have to consider the distinction between what is actually established, and what we 'know' only because a character said so.
Uninvited Guests
While I seem to remember the idea of Vampires requiring an invitation being talked about in the novel Dracula, I also remember him attacking Lucy in the house where we never saw him invited. So while the invitation rule may have roots that extend back that far, it was definitely The Lost Boys that popularized and almost universalized the idea that Vampires can't enter a home without an invitation. Most depictions of this rule are unintentionally hilarious, looking like bad mime routines, or in the case of Let the Right One In, positively gut-wrenching. But The Lost Boys movie taught us that Vampires can't come in without an invitation. Except it didn't. Remember, Max actually said "Don't ever invite a Vampire into your house, you silly boy; it renders you powerless," though powerless was quite an exaggeration, as we later see him impaled on a fence post in that very house. This is used as the explanation for why Max has a reflection, though I think it's quite a stretch to say that seeing that someone doesn't have a reflection is somehow 'power' (the power to detect they're a threat? ... eh). And we'd already seen Star fly up into Michael's room without an invite, plus all the Boys just waltz right in, so all an invitation does is bump up their already huge advantage.
Garlic Does Work?
When Paul saw the garlic floating in the tub, he said "Garlic doesn't work," but in the sequels, Edgar includes garlic in his Frog Juice cocktail, which could imply that since then he's learned that Paul lied or merely meant garlic has a much lesser effect than Holy Water, or had faced other strains of Vampire who are vulnerable to garlic, or like the raw eggs, the garlic is just part of his new health-kick. Just kidding. He also has a garlic bolo and in part three, they use garlic to keep the Alpha weakened. We also see around Edgar's trailer appears to be a huge ring of salt, which usually isn't a protection against Vampires (except some of the old folkloric Vampires who were believed to be so O.C.D. that if you threw salt on the floor, they had to count each grain before passing), so this may imply that Edgar's encountered ghosts or other supernatural beings as well, because that would be a lot of salt (see what I did there, Bible fans?) if it was just out of an abundance of caution. Or other strains of Vampires. The Vampires in the sequels have slightly different looks (prosthetics look grungier, and we see both black-eyed, and red-eyed Vamps), and I'd like to think a bit more thought went into it than "Let's make 'em look different."
So even if you only consider the official movies, there are some gray areas that make more sense if you allow for the idea of different strains of Vampires to which slightly different rules apply. The girl gang that butts heads with the Boys isn't from the same strain, but that is a tale for another time...