Collingwood Street, grave covers

Two medieval grave covers were found while a property in Collingwood Street was being pulled down in 1899. One was 20 inches long, 9 inches wide at the top and 8" wide at the bottom. A relief of a floreated cross, with the stem of a sword and buckler on one side, and a square on the other. The other was a gable cross, 18 inches across the arms, with a lamb in high relief in the centre. A letter from Messrs. Oliver and Leeson says that one is a grave cross of the late 13th century and one is an east gable cross of Early English work. Could these be from the early church of St. Nicholas?