I think you’re missing the fact that Daz Studio has also been in “beta” development along with Carrara, and that Carrara is being altered to work with Daz Studio and genesis, so, if something in Daz studio is added or changed, then that needs to be working in Carrara too. which means that the process can take longer than a single product being worked on.
EG: the new Duf format and DSON both have to be tested and proved to work in both applications.
Daz Studio,...still free. and more new users purchasing content. ...means more development potential.
Daz could just release Carrara 8.5 “as is”,. and then release updated versions ,.. like DS
but I think the majority of carrara users are prepared to wait until there’s a complete “working” version.
( I don’t think that’s far away, ..judging by the current 8.5 beta)
either way,. and to answer the OP’s question,.
There’s no “Free upgrades” policy. its up to the product retailer.
BUT : Daz3D normally have a sale, or offer period, to launch any new products, or version upgrades.
version Updates to a single version of a product,.. are normally free, (although they don’t need to be)
but technically speaking the work that has now been done on C8 to make it into 8.5 means that it’s a different program, and Not a version update,. it’s an upgrade.
Whether the Updates, and /or upgrades to products are paid for, or not,.. is entirely up to the retailer,..