ES-XW7T-1A278-AC is the same Ford engineering specification as its predecessor listed on this site, carrying the next revision suffix, and it is retained as a separate page only because the site records both. Two suffixes of one specification should be treated as one requirement in two states rather than as two documents: the core number identifies the subject, and the suffix identifies the amendment, so the later suffix supersedes the earlier. In practice a supplier should obtain the latest suffix, establish what changed from the one quoted in an older specification, and decide whether an existing test report remains valid. Where a programme is already in testing, the change is normally handled as a deviation or as a supplementary test rather than by repeating the whole programme. In a mature programme the revision change is usually handled by testing only the clauses affected, provided the difference between the two revisions has been established and recorded.