QR codes have several different bit-pattern masks, which an encoder should choose between to avoid blocks or runs.. so even without altering the URL there are d

QR codes have several different bit-pattern masks, which an encoder should choose between to avoid blocks or runs.. so even without altering the URL there are different outputs. [A-Z0-9] encodes a lot more efficiently than [a-zA-Z0-9] so there are other considerations when altering a url.