Mothers Tartan?

[gilmore]

The most reliable dating I have for the concept of wearing one's mother's tartan reaches all they way back to 19th century Scotland. I've never come across anything earlier in print, although a lot of 20th century academics and FSA scot-types seem to have spilled a sea of ink justifying the practice by reaching back into the mists of Scottish history.

...

I agree. Isn't there something inconsistent with using supposed practices of the matrilineal Pictish culture---which died out in or before the Dark Ages, even before the clans arose to which clan tartans are attributed---to shore up the wearing of what is largely a 19th Century construct?

What am I missing here?