In original source material – FR1, 1987 – the brass Waterdeep coin with a hole is called a ‘toal.’ In later material – Dragon Heist, 2018 – it’s called a ‘taol.’ Which spelling/pronunciation do you prefer? "Taol" is correct. The other name comes from outland traders visiting Waterdeep who assumed they'd misheard/misread, and it should be a "toll," just spelled oddly. In the streets of the Deep, you'll hear both…but saying "taol" marks you as a native, and "toal" as a visitor.
— Ed Greenwood (@TheEdVerse) October 10, 2018
And out-of-game, in-real-world: substitute "the 1986-era TSR secretarial typing pool of non-gamers" for "outland traders" ;}
(They "fixed" the MS. Several times.)— Ed Greenwood (@TheEdVerse) October 10, 2018