When you use Boost Sales to create discount offers for a specific product, it will create new variants with discount prices, corresponding with the original one. However, most of platforms allow each product to have maximum 100 variants only. Therefore, there would be the case when some variants of your up-sell/cross-sell products are not discounted when the total number of variants (original and new generated one) is over the limitation.
How many variants will be generated?
With a discounted up-sell product in your up-sell offers, the number of variants will be doubled. Let's take product X, which has 5 variants as an example, the new discounted variants will be 5 too, so the total will be 2x5=10 variants.
When you create a cross-sell offer of product A which has 15 variants and product B which has 20 variants, technically, you are creating (15x20=) 300 bundles. Each bundle will include 1 variant of A and 1 variant of B. By adding a discount price for your cross-sell offer, the discount price is applied for all 300 bundles. However, in order for Boost Sales to work smoothly, we limit the number of discount bundles by 200. Thus, from the bundle number 201 to 300, they will not have the discount price. We will have a notification when this case happens after you click Submit Offer and you are not able to complete creating the offer.
However you can use Sales Motivator to apply the discount, this feature will not generate any additional variants, here is the instruction for your reference.
Any further question can be sent to firstname.lastname@example.org.