I am also super curious about this, and I honestly can't tell any differences. If I had to guess, Pedro was never in the suit in season 1, except for the face reveal. Someone on reddit who said they worked on season 1 claimed that Pedro was never on set. But then we have quotes from Brendan and Pedro which seem to contradict that. Although could they have been talking about season 2? Also in the Talk Art podcast, Pedro said he would be in London until the beginning of December filming Wonder Woman, and season 1 of The Mandalorian was filming for all of November. If he didn't do any filming for half the episodes, why even bother having him in the suit at all? Also, Mando looks very slim in pretty much all the episodes, and Pedro did seem a bit chunkier during that time and had a bit of a tummy. But I feel like the easiest way to tell would be by looking at the shoulders, because Pedro has such broad shoulders. Time for a rewatch!