According to Roget's Thesaurus, few and several are synonymous, so it is not really a case of the one 'becoming' the other. What either means depends entirely on the context in which it is used.
If you asked someone for a few/several matches, you'd probably expect - and get - four or five. On the other hand, there were over three thousand Battle of Britain pilots and Churchill happily referred to them as "the few".
In other words, it's all relative. Personally, I would say either word correctly fits any number from three upwards, depending on the situation, so I'd be on your side as regards a couple, not your boss's.