Hi Sunic,
It is indeed a very old post. Sadly 11 years on I'm still no wiser as to Mary Verall. I have so often found that pre 1800 records are a matter of digging and hoping it all falls into place. My main research had been the Costers who began with William b. 1781 in Marlow. who moved to Eastbourne. Fortunately I live not far from Marlow, and was able to spend a lot of time going through church records but even so I only got back to about 1690.
I did however have a lot of fun with the Russia / New Zealand link mentioned in this thread and again it was a sheer luck thing. Found a dead australian e mail, googled the Australian phone book, rang a number and found a pile of Coster descendants in NZ, descended from a Coster sister who emigrated there. She had two sisters who were governesses in Russia to the Russian Royal family. The New Zealand descendants had letters from them but presumed they had both died in the revolution. I had to ruin a great family story proving they both escaped and lived to a ripe old age in Eastbourne.
Sorry I cannot be more helpful
Richard.