John, you wrote:

"One curiosity. She apparently signed her IOM marr cert to John Corkan, but made her mark on her marr cert to Henry Sidebotham. Any thoughts? Any other info, needless to say, very welcome! "

Here's a theory:

I wonder whether Eliza had so little schooling that writing her signature was the limit of her writing ability. She managed to write Eliza Sayle on her marriage to John Corkan in a small familiar church, but during her years as Eliza Corkan, she had no occasion to write her name, and perhaps didn't even know how to spell it. So, when faced with the prospect of trying to sign Eliza Corkan in a big imposing cathedral, she took the easy option and made her X mark.

Jean