Do I have to renew third-party assets' licenses when a new major version of Unity is released?

When I buy Unity, say version 4.x, and the new major version is released (5.x), I have to buy license again to be able to use features of 5.x.

However, do I have to re-buy paid third-party assets from the Unity Asset Store, when I decide to migrate to 5.x? Or is the license of assets ‘eternal’ unlike the license of Unity core? Or maybe asset owners have a choice?

There is a similar question in FAQ on the main website, but they say “assets need to be upgraded”. What does it mean in this context? Just download new software version or, no beating around the bush, pay?

There are no upgrade fees for assets. It would be completely insane for them to even think about requiring people to re-buy all their assets just because you upgraded Unity.

–Eric