My Aunt & Uncle, Phyliss Moore & Mark Robinson I was led to believe were married at St Silas in 1940. However, the marriage records for St Silas on this site do not show a reference.
The Free BMD site as I have sometimes found in the past can produce limited results.
Entering the name Mark Robinson gives you his marriage in Sheffield in the Sep qtr of 1940 to Moore.
However when entering Phyliss Moore a reverse response doesn't appear, just a 1936 wedding which is not relevant.
I concur, the church wedding is not on Ancestry or Find My Past, either they married at a church where records have not been transcribed or they married in the Register Office.
I find that occasionally on Free BMD, if an expected event doesn't appear in the search results, do take the trouble to look at the actual index page they provide, and you will find they have sometimes missed transcribing an entry on that index. Ancestry obtained FreeBMD transcriptions at an early point, and so these odd ones missed don't appear in Ancestry searches either. That is unless someone searching has pointed it out since then, and they've done an alteration/inclusion. I happened to my mum's cousin's birth, which was totally missed off.
Instead of searching separately for each name. Search for Mark and then click on the page number (in this case 1637) and this will show the other names on that page.
Register Office weddings are only available at the register office by buying the certificate.
Another good practice is to avoid being caught out by alternative spellings. If you searched for Phyliss you would not find it because it is spelled on the record as Phyllis. If you had searched Phyl* you would have found it.
Dave
Just to mention one specific useful feature of FreeBMD search. In a given name you don't need to put an asterisk at the end of an abbreviated name. In the above example Ph, Phy and Phyl would all have found the entry - it searches for anything beginning with the letters you put in (p on its own doesn't work because there are too many results).
You would have to put in an asterisk if you wanted to also search with a middle name or initial. For example, Phyllis E Moore born in Bristol in the same quarter can be found searching for Ph* E (space between the asterisk and second initial)