LeCun et al.'s two 1989 ZIP-code papers appeared in a bimodal order: the NIPS conference paper was presented first (Nov 1989), the Neural Computation article was printed first (Dec 1989), and the NIPS proceedings volume only appeared in 1990

LeCun's Bell Labs group published closely related handwritten-digit work twice in 1989: the NIPS conference paper "Handwritten Digit Recognition with a Back-Propagation Network" (Advances in NIPS 2, pp. 396–404) and the Neural Computation journal article "Backpropagation Applied to Handwritten Zip Code Recognition" (claim-lecun-1989-first-practical-recognition). "Which appeared first" has two correct answers, and citing "LeCun et al. 1989" without specifying the venue gets the sequencing backwards:

• By presentation: the NIPS conference paper came first — the conference was held Nov 27–30, 1989 in Denver (dblp: "NIPS Conference, Denver, Colorado, USA, November 27-30, 1989. Morgan Kaufmann 1990").
• By printed publication date: the Neural Computation article came first — in print December 1989 (Crossref published-print 1989-12, DOI 10.1162/neco.1989.1.4.541; OpenAlex normalizes this to 1989-12-01), Volume 1, Issue 4, pp. 541–551.
• The NIPS 2 proceedings volume that formally contains the conference paper was not printed until 1990 (dblp "Morgan Kaufmann 1990"; Open Library first_publish_year 1990) — a year after the conference, even though the NeurIPS archive retroactively labels it "NIPS 1989."

So: NIPS presentation (Nov 1989) → Neural Computation print (Dec 1989) → NIPS proceedings volume in print (1990). The "1989" on the conference paper is the conference year used as a citation label, not the volume's print date. See moc-backpropagation-origins.