Some years ago, I'd come across a surprising number of 'name ground off', but obviously Plomb, tools at the old San Jose 'Pulga de Sanjo' flea market, which I offered up cheaply on ebay, when ebay was new. Every one of those tools had some grinding/polishing flaw, unsightly when inspected closely. (I've no idea as to whether those were condemned before heat-treat, or afterward, so I never actually tried using them)
I don't have any first-hand information, as, say, from a retired Plomb/Proto employee, to be sure, but I'd think that the greatest likelihood would be that those tools were sold as 'factory seconds'. Whether the Plomb works might have had a 'factory seconds' store at the plant, or they sold them by the hundredweight to some salvage dealer, or whether the plant workers got to take them home, is an 'unknown', to me, at least.
At one time, the San Jose flea was 'deluged' with 'name ground off' Thorsen tools, which a Thorsen employee was buying up cheaply as 'factory seconds' and selling at the flea, and selling fairly cheaply.....and 'in volume' at the flea. Quite a few of the regular flea market sellers bought up quantities of those tools, and had them at their stands, for years afterward.
cheers
Carla