Despite the use of an -8 suffix, there does not appear to be any other size 64.
There is however a variant with a twig-handle (unusual for the Later Series) incised 64-8H.
Shape book 'A'
Collection; Shepparton Art Gallery
Gift of Dr.H.D.Chamberlain
The 'H' suffix denotes the presence of an applied 'twig-handle'. Such twig-handles are common in the Early Series, but here in the Later Series are relatively rare, being found on only a few shapes. This is one such Later Series shape with twig-handles. Others include Later Series 91.
In sales brochures showing selected Early Series pieces, items with twig-handles are labelled with the suffix 'H', but curiously the suffix does not appear on the actual Early Series pots - unlike here.
Collection; Lynne Cumming
Nicholnack art in pottery
A single pot with a different shape is recorded incised 64-10 but it is actually a Later Series 68-10 jardiniere with the wrong number.