I do give the edge to AMBERSONS for a few reasons—while it's true that LAM was in general release (something in its favor), it was a silent film, which within a few years time was worthless to almost everyone. Someone having elements/prints in their possession would probably be less likely to take care of an old silent movie.

It's been my experience, however, that certain films have a higher survival rate when they stay "in the family" of film makers. By that, I mean, if Bernard Herrmann had a scoring print of one of the original preview cuts, that print was more likely to survive in some way rather than someone who found an old print in a dumpster, possibly not knowing the significance of what it was. AMBERSONS seems to me, as famous as the cut preview versions were, to be a more likely candidate to be overlooked in context by a casual observer, since the film as we know it isn't lost today.

Plus, stuff that sits at labs, vaults, etc., seem to have a better survival rate than stuff that's out there in the open. Just a note.