This is covered in our FAQ: Common Questions, Adobe Stock
If I cancel my membership, can I still use any unused licenses in my account?
No. You can use your available licenses as long as your membership is active, but you forfeit any unused licenses upon cancellation of your membership.
Can I use the assets even after I cancel my membership?
Yes. Once you have licensed an asset, the license is permanent. You can use the assets you buy regardless of your membership status.
So it seems like the purchased credits must be used before the subscription is cancelled.
What is I choose not to take advantage of the Adobe Stock/Dollar Photo Club first year offer and simply migrate my credits over from Dollar Photo Club without signing up for an additional plan. Will I still get to use those credits for a year?
Yes, that's correct.
Migrated DPC credits will be available to use for 12 months.