Hi Hamlets,
I was in the National Archives yesterday, and did a quick query on the "Charlton Charity Certs". The guy behind the desk looked up a "miscellaneous Items" reference book he had, and asked me did I want Meath or Kildare, then asked did I want A to K or L to End. I filled a yellow Order Docket, with my name, Reader Card number, date , and Description, i.e. "Carlton Charity Certs, Meath , A to K.....waited 30 mins and was presented with a Box of the original certs, tied in bundles, that is an "A" bundle, a "B" bundle etc. This was wonderful if one wanted to pore through the certs, but not great if one was looking for a particular person. So ....
I then asked about any Finding aid or Index to these and the attendants did not know of any but offered me the the above mentioned reference book to look through myself . I discovered that there was a red volume labelled "AQUISITIONS 37" on the open shelving which lists over about 200 pages the "Longford Certs" and in a further 200 odd pages the "Meath Certs". , in Alphabetical order by the Husband. So if Armstrong, Patrick married Smith,Ann there is an entry under "A" but not under "S". In these two volumes there are 2,000 marriages listed in each of the two county sections. and the initial page in each 1796 to 1862. This should give you plenty to get your teeth into.
Very Important - I believe the rules for issuing a readers card require you to produce ID, ( eg a Passport) and a Proof of Address ( as a Utility bill or Bank Statement or Tax Man letter with your name and address on it).
Hope this helps to answer your Query. If I can assist further please let me know. Although I live in Dublin I am from Meath, so definitely do not qualify as a Jackeen,