Was “NG” originally printed on the previous gen aircraft, but later shifted to just 737-800/737-8? I always thought the MAX name was kind of like ”New” - ie something that would disappear.
The ‘classic’ ones were -300/-400/-500, and the NG were -600/-700/-800/-900. The MAX 8 is a replacement for the -800, and it has been called a 737-8 for a while – their FAA type certificates are 737-7, -8, and -9.