I have folk I cannot locate in the St Pancras area of Middlesex in 1851, and have searched by forename & surname, using wildcards & numerous possible variants, with and without ages and birthplaces etc etc, and also checked out known addresses and surrounding areas.
The lists of missing and damaged records at both Ancestry and FMP seem to cover only relatively significantly sized omissions - that is, they don't list the odd mislaid page, or the occasional dwellings that got overlooked, and so on. Also, some damaged records are held by TNA but were not filmed, so are not transcribed on genealogy websites, but don't show up in their known to be missing lists either.
Having said that, I've checked at the TNA website and found no mention of any missing or damaged 1851 census records in the St Pancras area where my folk were likely to have been.