I think the entries you have seen are from the marriage index - Microfilm 08828 / 05, the numbers in these indexes generally a sequence number noted in each actual marriage register entry, sometimes the indexes use the page number. In this case marriage register is on Microfilm 08834 / 03. The page which shows the marriage for Charles is 253 in the register - see towards the top of the right hand page. Charles McCormick to Ann McCoy at St. Paul's RC Dublin City (there's also a Church of Ireland St. Paul's) on the 13th November 1825.
The entry for that Dennis McCormick is on this register page, married Catherine Walsh on the 7th[?] February 1834, so unfortunately a little too soon after the marriage of Charles to be his son.
Edit : I see from a previous post that the parents of your Dennis are Charles/William Charles McCormick and Mary McDonald - do you know what denomination your McCormick family were ?