On the DEVONthink 4 upgrade purchase page, it says:
“Please note that purchasing an upgrade, e.g., to a higher edition, will trade your existing license for the discount and your old license will be deactivated in three months time.”
I’m not 100% sure what this means, especially as on the pricing page the FAQ states:
"When I upgrade to DEVONthink 4, do I trade-in my license?
No, all license codes for DEVONthink 3 remain valid and you do not need a new, separate license for DEVONthink 4."
That is accurate as it’s talking about upgrading editions. Different editions have different licenses.
"When I upgrade to DEVONthink 4, do I trade-in my license?
No, all license codes for DEVONthink 3 remain valid and you do not need a new, separate license for DEVONthink 4."
And this is also correct. If you have a valid version 3 license, when you upgrade to the same edition of version 4, the existing license is extended to cover 4.
Does this mean that if I upgrade my Devonthink v3 to Devonthink Pro v4 I will no longer be able to use my Devonthink v3.
However if I upgrade Devonthink v3 to Devonthink v4 I am still able to use my Devonthink v3 on another mac.
You can use also a DEVONthink Pro 4 license code on DEVONthink 3.9.11 and up, but it won’t give you two extra seats. Regardless whether you upgrade within the edition (Standard to Standard) or from one to another (Standard to Pro), you’ll end up with a license that covers two devices.