In all honesty, I wouldn't believe the numbers even if I saw her get on the scale.
She lies to herself more than she lies to anybody else. At that weight scales are inaccurate anyway and get more so as their maximum load is reached, so one weigh in is pretty useless. And we have no idea how the scales were tared, especially as she reaches her mental block of 500lbs. That's a really big deal to her for some reason, who knows whether she's tared the scales to "allow for clothes" or some other diversionary tactic.
I know that sounds extreme but AL's denial is extreme which is part of the reason she's always being caught out in small, pointless lies. She switches right onto defensive over absolutely everything and her immediate reaction to perceived attack is to lie, even if no attack was intended. The combination of that, her need to be a star in her own story and the likelihood that she's completely overwhelmed if she looks at any tiny fraction of her life because none of it works, its not that big of a stretch to her sabotaging her own weigh-ins to maintain the delusion to herself.
And, of course, nobody knows better than her. It really makes you wonder at what point will she honestly look at her life, even if we never see it? When a common cold turns to pneumonia? When she becomes completely immobile? When she needs oxygen because she gets out of breath from just breathing? What has to happen?
Fuck, she's frustrating.