Liberty Foundry

So here's a puzzle.  I was watering plants in the front yard before heading off to USC today - and looked, for the first time, at the little iron door (for what?) in the neighbors' wall.  It's labeled Liberty Foundry LA CA - and that, you'd think, would be easy to track down (I was mildly intrigued by the existence of Los Angeles iron foundries, presumably around 1929, when the house was built.  At least ours was, and probably theirs, too - it's a similar style).  But no mention of Liberty Foundry around then - at least not on line.  Penton's Foundry List for 1918 has a whopping 39 foundries listed in LA - not all iron - some are brass.  They locate Liberty at 3429 S Main, which oddly enough is just five blocks from my office.  But the Southwest Builder and Contractor (a fascinating source for urban history), vol. 51, March 29 1918 firmly lists Liberty Foundry, of the same address, under "Fictitious Firm Names" - whatever that may mean.  And was it still fictitious in 1929?  Or was this another firm entirely, by then - albeit one that's been very coy about leaving a digital footprint?  Almost certainly I won't be pursuing this further, although it did strike me that it would be a fascinating piece of sleuthing to track down where building supplies - and builders themselves - came from in LA in the late 1920s.