I know the brand, though not the model. In 1982 i bought a Caravan double-bag, 4 seasons (-30 C), which can be zipped together to be used as an 2 persons sommer sleeping bag.
The bag has been uses rather much and part of the down went out through the stitches. Because it is an stitched through model it could not be refilled.
Asked a good outdoorshop, they know about amount of down, temperature rating and also if you can refill the bag.
I still use my bag every suommer 25 years on a row and last year in winter (-15C)