Princess is slightly less generous with guarantee upgrades than other lines, due to the fact their room assignments are done entirely by computer. It depends on what category you book (the higher you are, the less likely of course), # of rooms in that level (they're notorious for significantly overselling BE and BF guarantees for example - there are usually few rooms in those levels, and they basically use it as a "run of category" <i.e., balcony>). Rarely will you see someone in a BE/BF get moved up into a mini-suite, but it's more common than not to find them in BC/BD cabins.
When Princess starts to assign cabins, they upgrade based first on past passenger status, then on date of booking and amount paid. They start at the top and work down, plugging in both guarantees and others at the same time. For example, if they have 4 BA guarantees they need to assign, they'll look at the categories above, and based on their formula of priority, move people up. Sometimes the people booked in the BA will have a higher "priority" than others with assigned cabins, and they'll get the upgrade preference.
Because Princess has so many levels (several levels of inside, outside, balcony, etc.), a 1-2 level upgrade within a general category isn't unusual at all - even 5-7 levels. It's far less usual to find true category upgrades, especially as you get to the higher levels. More likely to see inside>outside upgrade than balcony>mini-suite.
THanks so much Burbunny for your quick reply. I booked a BA guarantee on the Royal Princess. The Sailing is 9 months away and over half of the BA's are already assigned, whereas the next step up (AC mini-suite) is not sold at all yet. I was one of the first to book when the new schedule came out (according to Princess) so I can only hope that I will be one of the first to be upgraded. keeping those fingers crossed!
We booked a low-end inside guarantee on the Sea Princess on Nov. 2. The website shows that we received a II (highest inside) cabin. We haven't received the docs yet. Any chance we'll see a further upgrade? I'm happy with what we got but you can always hope!!