With the 16-digit displays, new for Williams with Taxi, straight away Williams decided to use it in 'extended' mode, driving an additional display. To do this, the circuit board was fitted out differently, using the alpha-numeric 'starburst' segments of the lower display for the additional display (or displays, Riverboat Gambler has two) instead. Doesn't the replacement offer this, even when ordering it?
If you're looking for an original main display circuit board, I think the version with 1 extra display was designated '-2' at the end of the part number; ordinary was -1, and two additional displays was -3.