Why do people think Mike Schmidt is Michael afton?

I thought the movie clarified that they are 2 different people?

There are only few coincidences and so many things that prove that they aren't the same people.

Coincidences:

• they both have 3 siblings (if you don't count Vanessa)

• Mike is the shorted version of the name Michael

• Both have a brother that was killed, but only one of them have a dead sister (if Vanessa doesn't die due to her injuries)

• both of them blame themselves for their brother's death.

Other things that prove they aren't the same person:

• Mike's brother was killed by William, Michael's brother was killed by the prank in 1983. William even says, "First I killed your brother, now you, symmetry my friend!" Which clearly implies that Garrett isn't BV/Evan/Dave/David/C.C/Whatever his name is now.

• Mike isn't related to William, in Mike's memory/dream of when his brother died, we can clearly see Mike's parents, William kidnaps Garrett so he can't be Mike's dad, because then he has to be in 2 places at once.

• Security log book just says Mike, this book belongs to. It doesn't say Mike Schmidt or Mike/Michael afton.

•Michael can still use the name Mike, it can be used as a nickname or a shortened name for Michael.

• Michael's sister's name is Elizabeth, Mike's sister's name is Abby.

Please don't just compare Mike and Michael, compare their families.

There are so many other things that disprove that they are the same person. However, I can't think of more.