OK, I've got a couple of minutes to kill. Let's try to knock some sense where none went before -
SilkLink wrote: which means that there isn’t a test case in law that disputes sending yourself a letter as a method of upholding your copyright, despite what other might say.
There are plenty. This nonsense with the envelope, as well as various private registration schemes are put forward by the foolish and judges keep throwing it out as inadmissible evidence.
SilkLink wrote: Say I come up with an idea of a song and somehow get it published – or at least send it to a publisher to get it promoted.
You are confusing publishing with publisher. You don't need a publisher to publish a work. You just have to get it out there, i.e. publish it and in such a way that the dates of making the work public are easily verifiable. GEMA, MCPS, printing/replication works and possibly even a distributor, iTunes and certainly Amazon would all be able to verify that a work was published at a given time.
SilkLink wrote:maybe that one of my verse lyrics are more or less the same to that of another tune, I may be tried for breach of copyright.
Now you are confusing civil and criminal law. This is a civil issue and you will not be tried for anything. You may find however litigation filed against you.
SilkLink wrote:I don’t think publishing a tune proves anything about copyright.
Read what I wrote - it proves the date of publication. No more and no less.
SilkLink wrote:You may still have to prove it is your work.
No, it's the other way about. In the case of litigation for injury or infringement of copyright, the litigant has to prove that the defendant did indeed infringe upon the litigant's copyright. The defendant does not have to do so intentionally. It may indeed be all his/her own work and he may even be able to prove that it was completely an original creation. That is irrelevant. If you come up with the same tune as an existing tune, you have infringed someone's copyright. All they have to prove, is that the tunes are the same and that their version pre-dates yours.