Is there a license file that needs to be added somewhere, or another file that determines the gallery image access and display?
No. As long as your gallery uses the Pro 'jbcore' folder (rather than the Lite version), then your gallery will be Juicebox-Pro (with no branding and no image limit).
It sounds like your problem might be due to caching (either server-side or in your browser).
First of al, try completely clearing your browser's cache before reloading your gallery's web page to be sure that your browser is fetching the latest gallery files from your web server (instead of using older cached ones).
If clearing your browser's cache does not help, then the problem may be due to server-side caching (your web server still serving up older cached files even after replacing them with newer versions).
Please check with your web host to see if they have server-side caching enabled on your hosting account and ask them if they would be willing and able to disable it from your hosting package.
Caching certainly has it uses but it can also sometimes be a hindrance to development.
I hope my notes above help to resolve your problem.
However, if you continue to experience difficulties, then please post the URL to your gallery's web page and I'll take a look at your gallery and let you know what I see/find.
Thank you.