The "newer style latch" as you describe it was actually used on the first approximately 100 Chiefs (the Baby Chiefs). It has also been observed as original on a few higher numbered guns like yours.
Some guns in the 7XXX serial range actually shipped earlier than lower numbered guns such as:
322X……shipped in December 1953.
46xx……shipped in Dec '54.
Obviously, there was little correlation between s/n and shipping dates.
My point is, your latch could be original. For one thing, to change the latch from a flat latch to a new style, the gun must be disassembled and the locking bolt that the latch attaches to must also be changed. The latches attach with different type screws.
So it's not a 5 minute job, but it could have been changed, there's just no way to know for sure unless the gun is owned by the original owner.
To answer your question, most Baby Chiefs 5 screw guns came with the 1st style flat latch until the 2nd style flat latch began to show up sporadically in the 25XXX serial Range:
1st style flat latch used only on the Baby J frame and K frame airweights:
Photo by jackvs1
2nd style flat latch began on the Improved I frames, Baby Js and K frame airweights just prior to the Models of 1953 New J frame shown here: