No tyres are almost never as wide as advertised. There are two reasons for this:
1) Rim width. A wider rim produces a wider tyre (measured across the widest part of the tyre, the bulge). Meaurements are according to a standard rim width used for ERTRO (European Tyre and Rim Organisation) classification purposes but your rim is almost never the same.
2) Weight Weenies. The scurge of the industry, these people weigh components on cocaine scales and then make decisions based on the lightest. Tyre manufacturers are fed-up with weight weenie editors choosing the best tyres in magazine "Shoot Outs" according to whichever tyre is the lightest, have evolved and now overstate the sizes of their tyres. In other words, their old 25mm is now a 28mm, for instance. This means the weight weenie editors now think it is the lightest 28mm tyre in the batch but actually, it is just an average 25mm tyre. This practice escalated out of proportion in a mini arms race. Some truce was called a few years back when one company, Avocet, said it will stop the practice. It subsequently went belly up or almost belly up. The rest of them still play this stupid game.
Having said that, a mm sizing is just nominal. You wanted a wide tyre and you got one. It doesn't matter whether it is 45 or 47mm. My next rant will be about the stupid mixing of systems - imperial and metric, on the same tyre i.e. 622 (mm) x 1.5".