It's not just variant spelling that's the problem. An awful lot of English BMD index entries simply did not get into the final central GRO indexes at all, for various reasons. A book has been written on the subject, "A Comedy of Errors" by Mike Foster, focusing on the marriage records, and highlighting just how incomplete the central index records are. It's why local projects by local registrars to index their own records online are increasingly important. Often you can trace certificates locally that cannot be traced at all in the GRO indexes.