Here’s what I know (subject to change):
Don Williams is running Passport Designs and Sonic Scores as separate companies. He does have the serial #s and registered email addresses of all versions of Encore etc. but expects the majority of those email addresses to no longer work.
Here’s what I’m guessing:
Pricing for new and upgrade licenses is a marketing decision—this is true for any company. Writing code for a new product such as Encore 6 that takes into account previous version licenses may take much more time and resources than are worth it (remember that 5 was released in 2008 IIRC). Though the name is old, this is a new company with no financial ties to the previous owners of the code.
I would not be surprised if there is no upgrade path from previous licenses. If the price for E6 is low enough, it won’t matter. What did I pay for the E5 Upgrade—$119 perhaps?