Scala this.type example and how to introduce some type level security against supplied values

thistype.scala

trait Person {
  type PersonType = this.type
}

trait CreditRecord {

  type Holder <: Person

  val amount: Int

  def reduce(h: Holder, reduceAmount: Int) = {
    val intermediateAmount = amount - reduceAmount
    new CreditRecord {
      override type Holder = h.PersonType
      override val amount: Int = intermediateAmount
    }
  }

  def print = println(s"CreditRecord(amount=$amount)")
}

object Bank {

  def issueCredit[T <: Person](p: Person, _amount: Int) = {
    new CreditRecord {
      type Holder = p.PersonType
      override val amount: Int = _amount
    }
  }
}


val person1 = new Person {}
val person2 = new Person {}

val credit1 = Bank.issueCredit(person1, 500)
val credit2 = Bank.issueCredit(person2, 200)

val reduced1 = credit1.reduce(person1, 100)
reduced1.print
val reduced2 = reduced1.reduce(person1, 10)
reduced2.print

//val mistaken = credit1.reduce(person2, 20) // pay attention to "person2" in parameters. This code would not compile
//mistaken.print