Jim,
As you well know by now, I was referring to, once again, that body of song that is largely common to all of the English-speaking world, 95% of which I can actually show you the broadsides for and again the vast majority of these the earliest copies were from the period 1750 to 1820. Many of them are actually about events which OCCURRED in this period. I fully accept your local marriage songs and political songs will have different histories, but they are not part of the corpus I refer to above. Just in case you get the wrong idea again, I am not devaluing the songs you mention or trying in any way to say they are not traditional.

Regarding sailors' songs. You ask me for evidence. On many occasions the songs that are about actual incidents have been traced back to an early broadside contemporary with the event. There is a LOCAL song to where I live (The Wreck of the Industry off Spurn point) which has been collected in oral tradition in various parts of the country. The broadside versions I have seen, the earliest is about 1850. The event is a true one which happened in 1819. After many years searching I found the original newspaper report and the ballad is almost word for word as in the report. This is one example among many.