Baby teeth eruption out of sequence

Last year I did some fact finding on the eruption sequence of baby teeth (i.e. which teeth appear first and then which appear next). All well and good I thought as sure enough our little man followed the statistical eruption sequence (if a bit late) - lower central incisors, upper central then lateral incisors (well one of them) ... then ... nothing for 6 months! I was beginning to get worried when I noticed some full on teething symptoms again (drooling, rosy cheeks, nappy rash, etc) but no tooth in sight.

Finally we realised that one of the first upper molars was actually coming through ... and not only that ... a few days later we spotted another one on the other side, then another two. So within a couple of weeks he suddenly had 4 first molars! All of them appearing totally out of sequence of course!