Can one plan be rolled into another later on in a prorated sense?

[#1]

Hello, I have been working with CS3 for ages and am finally at the point where I am needing to consider a Creative Cloud subscription of some sort. I'm undecided how to approach this and am hoping that someone can answer the following question. If I start by buying just the Photography package and then decide in a few months that I want to buy the complete Creative Cloud package, can the Photography be "rolled into" the CC suite or can my purchase price be discounted in some way in a prorated fashion? Thanks in advance to anyone who might be able to help.

[#2]

The only information I have is at https://helpx.adobe.com/manage-account/using/change-plan.html

[#3]

Thanks John, this was actually very helpful. 

[#4]

Photography Plan is a deeply discounted 12 month commitment. 

Technically, you must cancel plan A before you can subscribe to plan B. 

If you cancel plan A early, you will incur a 50% early termination fee.  But if you contact Adobe Customer Care and tell them you want to upgrade to the Full Apps plan, they will usually waive that termination fee for you.

Hope that helps.