You did notice something useful - the fact that words like 挨拶 contain kanji which pretty much only have a single use and are always or nearly always seen together (so should be learnt as a unit). There's nothing wrong, therefore, with remembering that as a compound it has 手偏 twice over, and that might jog your memory when you see the word in context, or stop you mixing up 挨 and 埃.