I would think that a check of the serial numbers should be date enough ...

Same comment in the other thread.

Not all instruments have a serial number when made.

Many have only a paper "paste in" serial number (see any Stradivarius). Such labels often disappear and/or are easily forged.

Many manufacturers have "died" without leaving serial number/date of manufacture records.

Quite a few very nice instruments have no identifiable maker, even if there is a visible serial number.

Most wooden instruments require some maintenance, and parts like ebony fingerboards, tortoise shell or ivory nuts and bridges, ebony tuning pegs, and the like make the original compliance with all the laws inconsequential if controlled materials have crept in later.

Nearly all endangered or threatened living or "formerly living" things are subject to import/export controls. Especially for wood products nearly all wood types are available, albeit sometimes in extremely limited quantities, via legal import. The current law does in fact - so far as I can make any sense of it at all - make a "once illegally moved" material or articles made from it "forever illegal."

And, again what I understand of the mess, it is illegal to import anything that is not legally exported from the source country as determined by the export laws of the source country and/or as determined by the import/export laws of any intermediary country as determined by that country, or as prohibited by the import laws at the destination as determined by the laws of the destination country. Once "illegal" under any of these multiple sets of (sometimes conflicting?) laws the material itself and anything made from it is forever illegal.

But I'm not really sure what the portions of the most recent laws that I've been able to access actually do intend to say (and the enforcers may not understand them a lot better than we do).

John