Not 100% but, my understanding of Tarmacadam is that it is self sealing - the Bitumin that binds the gravel is the "sealer".
There are 2 obvious problems with most cowboy installations; either the groundworks haven't been done properly and all you have is a lovely black top coat and nothing of substance beneath (fur coat and no knickers) or else they didn't use proper Tarmacadam and only used "cold mix" which is only designed for temporary use e.g. potholes or temporary backfills to make a footpath safe until the concreting guys get aroud to finish the job properly.
Was the Tar very obviously HOT when it was laid and stay hot for most of the day after it went down?