Maltose Nomenclature
Maltose is 4-O-α-D-glucopyranosyl-D-glucose.  The "O" in "4-O" indicates the attachment of atom of the substituent.  The substituent in this case is "-α-D-glucopyranosyl".  It is attached to the oxygen atom that is attached to carbon 4 in the base molecule.  The base molecule in this case is "-D-glucose".  "4-α-D-glucopyranosyl-D-glucose" could be interpreted as a different structure where the &alpha;-D-glucopyranosyl substituent is bound directly to carbon atom number 4.

The "base molecule" of "-D-glucose" still has an unsubstituted anomeric OH group.  Thus, in aqueous solution, maltose will be an equilibrium mixture of at least these three isomers:


4-O-α-D-glucopyranosyl-&alpha;-D-glucopyranose
4-O-α-D-glucopyranosyl-&beta;-D-glucopyranose
4-O-α-D-glucopyranosyl-D-glucose (open chain on the right-most "glucose" moiety in the name)


Thus, it doesn't really make sense to disambiguate &alpha; vs. &beta; vs. open-chain forms of the "right-most" glucose ring in maltose, unless you need to refer to a particular conformation of maltose that matters for a certain reaction or condition.  However, the "left" ring is locked (in maltose) to an &alpha;-D-glucopyranosyl conformation because it does not have an anomeric OH group and rapid equilibration in water does not take place.