The 2023 date offset in a Vela X-1 BAT ASCII table also occurs in its FITS table

A prior SCI study found a one-day date offset in a Vela X-1 Swift/BAT ASCII pointing table. We extend the check to its FITS table with files retrieved on 22 October 2026. All 2,396 pointing rows labelled 2023 have an integer MJD one day after the date from YEAR and DAY in both formats. Their time and date arrays are equal. Nominal mission elapsed time agrees with the calendar day. Conversion from the FITS TT reference changes the nominal time by at most five seconds. It cannot explain the full-day offset. All 6,654 daily-file dates agree with their calendar fields. We also reproduce the better agreement with daily rates when pointings are joined by calendar date. An illustrative one-day time error changes membership in our phase window for 494 of 2,396 rows. A separate planned fixed-interval spin test retains only one later spin-up and one spin-down interval, so it cannot establish a general brightness contrast. We preserve raw files, source hashes, a row-level date table, all test variants, figures, and code. The date result applies to these saved products. It does not identify the cause or establish a new physical event.

Vela X-1 · Swift BAT · Fermi GBM · data quality · Modified Julian Date · time consistency · accreting pulsar · reproducible research