Each chicken is different, they have their own personalities and behaviors. Reading on this forum you can get the opinion that all chickens all do the same thing. They don't. There are signs that a pullet MIGHT be getting ready to lay. There are signs that a hen MIGHT be broody or going broody. There are all kinds of signs but they are just clues that something might be about to happen.
Squatting is one of those. Not all pullets squat before they start to lay. The reverse is also true, squatting does not mean they are about to lay. I once saw a 13 week old pullet willingly squat for a 13 week old cockerel. She did not start to lay for another two months.
The bright red combs and wattles are a good sign. That vent check can give some strong clues, probably the best in my opinion. Seeing them in the nests scratching around and checking it out as a nest is a good sign. The pelvic spread check can give clues. Squatting is a good sign too. But these are clues, they might mean you are close but again they might not.