Two things about this fine under-used word:
1) Fact: Its current-usage frame of reference stops at the year 1500.
2) Probability: Its current-usage users are no more than fifteen gaunt and over-used academics.
This fine word, which you know is crying out to be commandeered into broader and more common current parlance, is anglicized Latin for “swaddling clothes” or “cradle” and can refer to “the earliest stages or first traces in the development of anything.”
OK. How about the the earliest stages or first traces in the development of a poet?
I propose that we re-coin, re-deploy “incunable” to mean “first book of poetry.”
Only one Incunable for everyone, to be referred to in endless bildungs-narratives, entered into endless Incunable Contests and cited as proximate cause in endless career-path ex-/im-plosions.