How do STOVL and V/STOL aircraft differ?
To put it simply, it's about the ability to take of vertically at any mass:

V/STOL aircraft can take off fully loaded (max. operational weight).

STOVL aircraft does not have sufficient engine thrust to take off vertically at any weight, and at higher T/O weights it must have some lift from wings to assist the T/O. It may be able take off vertically at less than max. T/O weight.