Not to sound cynical or stand off-ish, but I wouldn't put much faith in any dates for anything in CMA oral tradition because they often change. Then of course there is the dubious nature of the existance of the Nam Siu Lam Gee (southern shaolin temple), couple that with spurious dates and you'll get a rather annoying research experience. Just the story of Wang Lang alone has a 200-400 year gap, because the exact time between the two dynasties he lived is not known (one of which was a dynasty which extended to 1911).
Now one thing that needs to be taken into account is the specific lineage of praying mantis. The date inaccuracy above only takes into account the founding of mantis and is not taking into account the varying origin dates of the other types of praying mantis such as Seven Star, Tai Chi, Plum Flower, Six Combinations, Flat Plate, Secret Door, Jade Ring, Dragging Hand, Eight Step, Jut Sau, etc. So if further depth has to be reached, we need to narrow it down to a specifc lineage of praying mantis so we can streamline the discussion.
However on a geographic level, a preponderence of the practitioners of northern mantis were found in the Shandong region- nowhere near Fukien. This is obviously not to say they didn't spread, but the existence of northern mantis is not very prevalent in the south. I'm also basing the emphasis on northern mantis from the video- which doesn't show ANY remnant of southern praying mantis at all. So i default the overall larger lineage to at least some variant of northern mantis.
I personally feel that no validity can be placed on anything coming out of the Fukien Shaolin temple, not because there is no proof it existed (most of the legends based from this temple have roots in martial pulp fiction novels), but there are systems within SD that are basically in no way affiliated with arts that lay claim to a lineage to a southern shaolin heritage- i.e. tai ji, bagua, hsing yi, govt produced forms, Hua boxing, etc. Even going by commonly told stories of the southern shaolin temple, the abbots of said temple stopped after the displacement of Gee Sin and his compatriots. There is no mention of the patriarchs of the SD lineage.
So I would rather put weight into an entering date by a person that can be recognized within the same mantis lineage from which the SD forms originate. That way, if there is record of said persons exploits, it can be cross-referenced with the other lineages. Not only would it show where the form came from, but it would also give insight as to where and when that person would have entered a temple.
Peace