Yes, Bill and Will usually refer to WS and Ed to ES. Scottish words turn up frequently in barred puzzles, and are usually indicated by a place (eg Perth, Ayr or just 'far North') or a name we associate with Scottishness. Obsolete and rare words should really be indicated as such in the interest of fairness, as are dialectical usages ('in some parts' for example). Words from other languages which appear in Chambers (and American spellings) are also fair game, and they can have similarly appropriate indicators (eg 'Uncle Sam's' for an Americanism)
Sorry to go on !
C