Dating precisely is not something we can do, for the reasons Rich mentions above. What we can do though is date by association with other serial numbers, some of which we have additional dating evidence for, in terms of warranty booklets etc and also the dates certain models were introduced.

I'd beg to disagree with Rich a bit on his estimate - for me, 72/3 is far too late for a 166xxx watch. The first Monacos are 157xxx and from 1969; there is some disjunct between numbering ranges of various models at this time, that later settles down a bit. I'd be fairly confident about putting a 166xxx watch in 1970 - we've seen manual wind Monacos as low down as the 164xxxs but yours will still be quite an early example of the model.