It was 19-umpteen. A lot of engineering was based on rules of thumb and common beliefs. The baffle might have been intended to address a problem that did not exist, to address a problem that did exist, but ineffectively, or to address a real problem effectively. It is very unlikely that anyone then would have bothered to _test_ which of those it was.
Even now, where a car company might have more test vehicles than a total pre-war production run, a lot of stuff gets put in on the basis of "it probably does no harm" or a quick back-of-the-envelope FE analysis.