They probably do have reasonabke checks in place, likely done manually when applying. Just because the computer doesn't have it in a searchable database doesn't mean the system as a whole doesnt know
I obviously can't know why, but apparently the system allows to keep receiving benefits without the date being present in the database and maybe even claim benefits without the date being present, which is why.
Maybe the data was there initially, but was deleted or lost for technical reasons, for example the date was incomplete, e.g. only the year of birth was known, but not the exact day and then was dropped to null as invalid during some kind of upgrade.
Maybe the data was not possible to enter into the system for technical reasons -- somebody didn't have access, something was down, the next shift was supposed to enter it once the system was back up. Maybe the same, but for process reasons, for example setting the date requires attaching the birth certificate and the birth certificate is lost.
Maybe the data was intended to be entered, but somebody forgot to actually do it, was waiting for birth certificate to be produced, but approved the benefits provisionally.
Maybe the birth certificate was shown to the official, but was of the wrong kind (handwritten extract, foreign document without consular legalization, damaged, illegible or incomplete date), so it was legit enough to start paying benefits but not legit enough to upload to the server. Maybe the date was conflicting with other records somehow. Maybe there was a court decision involved which determined eligibility for benefits but didn't determine exact date of birth.
The key point here -- the system allows for this kind of inconsistency (benefits are being paid, but the date is not present) and relies on a human process to eventually reach a consistent state, but the process failed and nobody really cares to rectify it as long as benefits are being paid.
That's assuming the benefits are actually paid to those people and the organization is not aware of this data issue and not investigating those people for fraud right now.
In an organization big enough there is always this kind of stuff happening (see "seeing like a bank"), which is tolerated as long as statutory task is not compromised.
This still seems bad to me because the SSA should not be concerned with actual DOB, only DOB for the purposes of SS benefits. This will be actual verified DOB in the vast majority of cases, but we are talking about edge cases here. If the SSA determines, by whatever procedure, that someone is eligible for retirement benefits (meaning that they are determined to be over 65), it is incredibly sloppy not to insert some DOB in the SS DB.
Of course it's sloppy to not have any date in the DB. The thing is -- we don't know why exactly it happened and what kind of procedure they follow or don't. Maybe there is a scan of the certificate somewhere and it's illegible and nobody cares, because it's not a problem really. Benefits are mostly being paid to people eligible and any effort to achieve better quality will waster more money than is lost to fraud. That's of course triggering every autistas mind, but so what?
It could also be that entries in the DB that are complete are not exactly correct or even belong to real people and of course there is fraud and corruption going on at least somewhere.
The cost benefit calculation is, of course, reasonable. But there are 2 things that need to happen here.
1. Run a complex process requiring human intervention to determine age where it is hard to determine
2. Enter the result of step 1 in the DB
And it's pretty obvious that 99.99% of the cost of this is coming from step 1. So I find it completely implausible that just tracking the results here, when a single error could potentially result in a loss of hundreds of thousands of dollars, is not cost effective.
