I bought the last of the content I didn’t already own tonight (inspired by the sale), but was confused to find that the bundles are still on the shop, and have values attributed to them. I checked under the source book and adventure categories, and both told me there was nothing left to purchase (other than the pre-order for the new source book). To be clear, I bought it all as separate books, as it was marginally less expensive than buying it as a bundle.  

The legendary bundle is listed for $18.89, the sourcebook bundle is $12.02, and (most confusingly) the adventure bundle is listed at $23.11.

The only reason I’m bothered is I was looking forward to the 15% discount on future content. Are customers only eligible for this if they buy the bundles, and it is not related to owning all content?

There are a few things to note

• The price of a bundle is only reduced by the money you've spent on the books contained in that bundle, not their current price or the fact you own them
• You are only granted the persistent discount if you purchase the bundle

Here's an example that explains how it all works

Say you've got a bundle with a 10% discount that contains 5 books
That bundle will cost $134.95
If you buy two of those books at 25% off, the price of the bundle will be reduced by $29.99 * 2 * 0.75, making it $91.45
If you were to buy all four books individually, the bundle would still cost you $44.98, even though you're not buying any books
That $44.98 represents the difference between what you've spent and the price of the bundle
What it gets you however is a 10% discount for any future book added to that bundle

I suppose that makes sense, though I’m still confused to why an empty bundle would cost nearly $20.

I did check the price differences between the bundle, and adding the books up, and the books did come up cheaper. The ad i saw on the ‘gram also had a note stating that bundles were excluded from the sale.  

The empty bundle costs $20 because there's a $20 difference between the price of the bundle, and the amount you spent on the books found in the bundle.

If a bundle contains 5 books and costs $100, and you buy each of those books on sale for $80, you will get $80 towards the bundle. Although you now own every book in the bundle, you have not purchased said bundle itself (the bundle being its own entitlement) and you only have $80 credit towards its $100 price.

I think I understand now. The bundles are clever enough to know what money was saved on individual purchases from sales that excluded the bundles.

If I want that automatic 15% discount, it seems I’ll have to pay that ‘dodged’ cost. Might need to work out if it’ll be worth it in the long run or not.