I feel like I'm missing something obvious... I have a custom field (B) whose value is derived based on the value in another custom field (A). Works perfectly in the UI. However, when I set field A with a record.setValue in a beforeLoad, the sourcing doesn't run on field B. Is there a parameter on the setValue I'm missing or anything like that to make it work?

standard for beforeLoad in general

That's what I was afraid of. Thanks @battk!