'next' is a relative association....in this case, 'next', in reference to any day of the week, is relative to 'this' day of the week.  In the context of days of the week, 'this [one]' always precedes the 'next [one]'; in other words, when someone says 'next Saturday', the presumption is 'NOT this Saturday', because if they meant 'THIS Saturday', they should have used the word 'this'.  'This' can never refer to the most recent one, as the most recent day of any week is always referred to as 'this past [SMTWRFS]'.  So logic suggests that 'this' always refers to the most immediate upcoming one, and 'next' is the one that follows it.  But in order to avoid ambiguity and confusion, it's always best to clarify by emphasizing "not THIS[SMTWRFS], but NEXT [SMTWRFS].