What's to stop someone from lying about having retreated?

[Nuclear Unicorn]

Supposedly, one of the arguments against Stand Your Ground (SYG) laws is that it allows a shooter to claim -- presumably falsely -- they felt threatened and thus acted in self-defense.

The survivor gets to tell whatever story they desire, the argument goes, while dead men tell no tales. Thus, the thinking goes, we must abolish SYG laws in favor of Duty to Retreat (DTR) laws.

Leave aside for the moment the fact that witnesses and physical evidence are still a factor but consider that a person who would lie about having stood their ground would be just as motivated to lie about having retreated.

Apart from eroding the right to self-defense itself I don't see the purpose of abolishing SYG.