I noticed though that the Boxwood leaves does not have the white border unlike the Serissa pics you've attached. Is this true for all types of Serissa and Boxwood?
Nope, it is not true for all Serissa Phoetida varieties, but is rather common that the leaves are usually variegated as said
here
: "A small shrub from southeastern Asia, with very small leaves, little white flowers and trunks with a light bark. Some cultivars have variegated leaves. When the plant is pruned there is a displeasing smell." Oh, another way of identifying whether it is a Serissa or not is by foul smelling when crushing its bark or pruninig its branches and leaves.
As for Boxwood, yes it is true for all species as stated
here
: "Buxus is a genus of about 70 species of evergreen shrubs and occasionally small trees found in habitats ranging from rocky hills to woodland in Europe, Asia, Africa and Central America. The leaves of many Buxus species are very small which is an ideal attribute for bonsai. In Spring, Buxus display a show of male flowers with inconspicuous yellow anthers that surround single female flowers.
The two Buxus species that are commonly seen as Bonsai are Buxus microphylla/ Japanese Box and Buxus sempervirens/ Common Box. Outwardly both of these species are very similar, carrying elliptic, glossy, dark-green leaves to 2-3cm long. The main difference between B. sempervirens and B. microphylla is their vigour; B. sempervirens can reach eventual heights of 5metres with a spread of 5metres, B. microphylla on the other hand is very slow growing, only reaching an overall height of around 75cm with a 1.5metre spread."