Smartful is definitely a rare word. As you demonstrate, TRex, it's in Wiktionary and the OED. I found a few usage examples from the early 20th century, but none more recent. For example, this from
America and England (1913) by Celia Richmond:
They were all immensely excited, and they had bunches of flowers to throw at the bride, rice having gone out on account of its being dangerous for the eyes and very smartful generally.
I'll add it as a rare word.