When I examine my other galleries turns out some have jbcore folders, some don't.
All galleries use a 'jbcore' folder (the 'juicebox.js' JavaScript file will be loaded into every web page than contains a Juicebox gallery). However, it is possible that not all Juicebox galleries will have their own 'jbcore' folder.
Galleries that are on the same web page will share a single 'jbcore' folder and gallery that are not on the same web page can share a single 'jbcore' folder. (Please see the Using an External jbcore Folder support section for details.)
Every gallery created by JuiceboxBuilder-Pro will have its own 'jbcore' folder but I do not know how you embed your galleries into your web pages and if any of your galleries share a 'jbcore' folder.
All galleries that share a 'jbcore' folder will also share a password (in the 'jbcore/pswd.php' file).
When you edit the 'jbcore/pswd.php' file to change the password, be sure to use a plain text editor such as Notepad++ (not a word processor or rich text editor which can introduce hidden formatting and break the PHP code) and add your chosen password (or passwords) in the $passwords array. Also, make sure that you use regular double-quotes around each password (rather than other characters such as angled quotes or backticks).
You should be able to tell where the 'jbcore' folder for a particular gallery is located on your server by checking the source of the gallery's web page in your browser and looking for the <script> tag that points towards the 'juicebox.s' file.
If you're having trouble with a particular gallery, please post back with a link to it so that I can take a look for myself and hopefully help further.