13-56 should work fine on a 12-string tuned to D. The little warranty/advice booklet from Guild, in the 70s, recommended tuning to E only with light gauge strings (by which they meant, I'm sure, the ones now sold as XL, ie, 12-47) and tuning down a whole note with anything heavier than "light."

Personally, I wouldn't tune 12-47 lower than D in any case; the only set I ever used were 'way too slack at C#.

13-56, which most mfrs call "Medium" but mine (Darco) brands as "Light," does fine at C#, the highest I've ever had my cheapo 12-string tuned. It should be OK at D, but I can't say from my own knowledge. A friend had an Ovation 12 back in the 70s and tuned it to E with 13-56. I haven't seen him in years and don't know how it held up, but it seemed pretty stable at the time. However, I'm from the McTell school and prefer a much lower tuning.

13-56 is good for C#, not bad for C, and tolerable at B (which is where I keep my 12) when the strings are fresh. As they get older and stretchier, I find myself tightening it up a little, first to C, then to C#. When the strings feel slack at C# I know it's time to change.