A parent product has multiple variants. Some variants are on sale and some that aren't. This is a very common ecom practice for larger business. Some items with the family may also be on Clearance. So, it happens more often than not.

let's assume the lowest priced variant in the Product family is not on sale.

In this scenario, PDP shows the correct sale price for the variants included in the promo, and shows the original price for items that is not included in the promo but the PLP does not.

PLP is not considering the fact that the lowest priced variant in the family is not included in the promo, and applying the discount to it and showing in the PLP. This is incorrect. The PLP price should show "Starting From" or "Price Range" based on the lowest Sale or Original price instead of assuming all variants within the family is on sale.