I have since discovered that Camping's 2011 predictions of the end (that's right - there were two of them for that year alone, in April and October) were indeed also 'guaranteed'. The inference must be that the May 20th guarantee has about the same value, which is to say, roughly zero.
Now that really is a revelation. But what's this? Only 22 days to go before the worthless nature of these guarantees is confirmed yet again?
I hope you are all managing to hang on to the edge of your seats. And stop biting those nails.