I've worked with data similar to what you are talking about many times, and I cannot stress how important this is. Between record version type, this should change as well. You can tie this in to specific record related information like what the delimiters are, or record length.

Record labels accomplishe 1 key thing that trumps everything else you have said: You can write a parser for a single record w/o trampling over other record types. Without this, you will have no way to determine when data starts or ends between records. You would have to write some complex code to figure out record delimiters which may or may not be consistent.

It gets ugly fast, especially if someone creates a new record format w/o telling you.