What if there is no date on a lady liberty quarter?

It significantly affects the value. Standing liberty quarters prior to 1925 were struck with the date as one of the highest points of the coin, because of this the date, like on buffalo nickels, quickly wore off. About the only thing you can do is see if on the reverse if there are stars underneith the eagle, if there are stars on the reverse under the eagle it was made from 1917-1930, (though, if the date is worn off and the rest of the coin seems fine, you might be able to make a guess that it is pre-1925) if there are no stars on the reverse under the eagle it was made from 1916-1917.