Old.transformers won't always make board triggered whistles blow, (and visa versa)
Adding a diode type button (can be made and can do bell too or be added for bell only) or swapping out the Lionel whistle disc fora heavy duty diode (good for most post war, but 99% not 100%.
I.e. some whistles are just finicky (1 old and one new are finicky out of about 25 o mine)