Photographic Precovery of the Dwarf Planet Candidate 2026 ED138 on 1954–1991 Schmidt Plates, and a One-Day Offset in SuperCOSMOS Plate Dates

I report four positions of the dwarf planet candidate 2026 ED138 from digitized photographic Schmidt plates: Palomar POSS-I (1954), ESO (1982 and 1984) and UK Schmidt (1991). The images were found in SuperCOSMOS scans and measured against Gaia DR3. Each is within 3.7″ of the current JPL orbit, and on the three unblended plates the image is elongated along the predicted direction of motion. On the 1991 plate the object lies 3.1″ from a G = 17.5 star and was separated by a two-source fit. On all four plates the observation dates in the SuperCOSMOS archive are one day early; I confirmed this with known asteroids on the same plates. Users of SuperCOSMOS plate epochs for moving objects should check for this offset. No usable images were found from 1992–2009. Before 1954 the object (V ≈ 18.8–19.1) was too faint for any digitized plate archive. With the earlier VVV positions (doi:10.5281/zenodo.23740113), the observed arc now spans 1954–2026. The search, measurements and submission to the Minor Planet Center were all completed on 2026 October 29, one day after the 2010–2011 VVV positions were submitted. MPC submission IDs: 2026-10-29T11:57:52.333_0000CI1I (code 809), 2026-10-29T12:06:56.250_0000CI1M (code 260), 2026-10-29T12:16:33.246_0000CI1R (code 675). The submissions have been acknowledged but not yet accepted. Files: the note (PDF); the positions in ADES PSV format; and an archive with the SuperCOSMOS catalog extracts, SkyBoT lists, ephemerides, figures, analysis code and LaTeX source. Use of AI tools: the archive searches, analysis code, measurements, figures and text were produced with substantial help from Claude (Anthropic; Claude Opus 5.5 via Claude Code), under the author's direction. The author reviewed the results and is responsible for the content. Not peer reviewed.