Linked from a comment in the languagehat article is the Wikipedia talk page for the "Burmese alphabet" article, which puts that claim into doubt: https://en.wikipedia.org/wiki/Talk:Burmese_alphabet#Glyph_in...
If I don't return before the reply window closes for this thread, check Wikipedia for those who encounter this thread in the future.
Regardless, thanks for the post, I really enjoyed a peak into Pearl and Martin’s work, and yours.
Glad you like the stuff; always up for people having the specific link.