Yes they were.
I haven't had my 128 or 512s powered up for a while but I seem to recall that the 64K ROMs provides a slightly different boot screen (ie more traditional MacOS 6.x double line boarders vs shadowed box on the 32K ROMS).
I also have a vague memory of the About Mac window displaying the amount of RAM available on early MacOS versions (Bottom right corner? My memory is quite vague here).
I have a number of 128 boards that have been upgraded to 512 by hand. The easiest way to tell (on mine) is to look at the solder pads (ie not uniform as expected from an automated assembly line).
Remembering the cost of the 512 upgrade board back then, it was cost effective to get a technician to do a RAM chip upgrade on an existing board (at least in Australia back in the 80's).
Regards,
Macdownunder