> The kind of stuff found in the Pepys and Roxburgh collections of broadsides from the late 17th century is indeed unsingable, at least by today's standards.

Maybe by period standards as well. Relatively few went into tradition (oral or otherwise), and it's likely that the vast majority were rarely (or never) sung at all - at least as printed.

The same goes for the 19th century broadsides, no?

Not to mention 99.99% of songs since.