Back when I used to strictly hand-wash my jeans, I would notice they would occasionally get musty after not long, or if I didn't wear them for a while. Turns out, I just wasn't doing a good enough job rinsing out the soap. YMMV.
I wouldn't assume so, but at some point, Samurai started (randomly/per lot?) sewing their cuts with a raw waist measurement that matches the size e.g. that size 38 may have been 38" before shrinking, instead of shrinking to 38".