"this is the June 2020 version, this is the current version, we have no back ups in between" is acceptable if true. Destroying or omitting an existing version is not.
For a civil action, the burden of proof is "preponderance of evidence," which is a much lower standard than "beyond a reasonable doubt." "Maybe the weights are different now" is a reasonable doubt, but in a civil case the plaintiff could respond "Can the defendant prove the weights are different? For that matter, can the defendant even explain to this court how this machine works? How can the defendant know this machine doesn't just dress up discrimination with numbers?" And then it's a bad day for the defendant to the tune of a pile of money if they don't understand the machine they use.
Seems like the behavior becomes predictable and then you have to retrain if you see unoptimal results.
You just run the same software (with the same state database, if applicable).
Oh wait, I forgot, nobody knows or cares what software they're running. As long as the website is pretty and we can outsource the sysop burden, well then, who needs representative testing or the ability to audit?
There are three major kinds of evidence that would be useful here. Most useful but least likely: email inside the company in which someone says "make sure that this doesn't select too many people with disabilities" or "it's fine that the system isn't selecting people with disabilities, carry on".
Useful and very likely: prima facie evidence that the software doesn't make necessary reasonable accomodations - a video captcha without an audio alternative, things like that.
Fairly useful and of moderate likelihood: statistical evidence that whatever the company said or did, it has the effect of unfairly rejecting applicants with disabilities.