Three consecutive slows are actually pretty rare
I know what you're trying to say, but I think you should be careful how you express things to a beginner! Actually, in American tango, having three slows in a row is VERY common - for instance, whenever you string two 8-count basics together (S S Q Q
S S S Q Q S). In terms of how American "patterns" start, I think you're quite correct: starting with 3 slows in unusual, and I know of no basic pattern that starts so. However, In
Argentine tango, I think virtually anything is acceptable, and improvisation is part of the very essence of the dance. About International style, I know next to nothing, so I'll shut up....