I have no claim to being an expert on this, however the mitred corner indicate to me that it would be from a more recent time, from what I have been told the original guillotines from early 1900's are not at all suitable for cutting finished timber and were used to make base frames. That probably doesn't help, but hopefully spurs someone on with more detail!
Lance, a crude back saw in a miter-box would have worked just fine at either time period that I asked about.
Length moulding starts rearing it's head in the early 1800s with the Empire push to make the art into a craft.
The early guillotines were nothing more than shears that shaved the ends to the perfect mirror of a miter.
There is a lot of hubris by a general society about the "crude" days of yore.... which is why we go to museums
to marvel at tables made for Louie XV, or fine furniture in the Vatican that dates to the 14th C.
If the moulding in question is from the Barbazon period of French Revival, the moulding would have been chopped and mitered
and then the compo laid, followed by the holes being bored. Exactly the same way it would be custom made today as a closed
corner. But if it comes from the Experimental days of the early 20th C, then the moulding would be shaped, and bored, with
the plaster applied wet after. The chopper I learned on was a 1926 production Jyden. It worked just as well as the 40 year old
Morso I work on today. But I do hear a lot of smack talk about some of the new blades, and machines that don't stay adjusted.
The "miter chop" and join dates back to the original Cassetta frame of the 1400s. While the auralists loved the hand carves swirly
corners, the Mannerists wanted a more Teutonic architectural look and created the Cassetta. But the miter was done much the
same way I do my own hand made cassetta frames. Hand saw to about 45 and then sliding hand plane to the perfect corner.