As long as it's true it doesn't matter what order or format it's in
at the early statges of a case or investigation that may be true. However, if being used in formal criminal proceedings the statement must have a declaration from the witness that he understands that if it is false and it is tendered in criminal proceedings he will be liable to a fine or imprisonment; in civil proceedings it requires to have a "statement of truth". I suspect that this is very early stages so what they are after is an initial account. However, if called upon to later make a more formal statement it is important that the two do not contradict each other as both will be discloseable in any proceedings.
The point about self incrimination still stands though, irrespective of the form of the statement.