Hello there Tom W ,
Thats cool that it didn't fall out ,my brake setup( I still have them in the garage) look different .If your shoes are indeed kept adjusted out I can see
that it may not fall out .That doesn't change the fact that they most certainly do alot of times as mine had .Many do not keep up on adjustments or maintenence on there trailers so I see this fairly often,and it doesn't take
much clearance for this to occur .Old brake springs need to be replaced ,not
just the magnets or shoes ,again ,better to get new and be done with it .
perhaps that adjuster in the photo is stuck in the shoe tabs ,I can see that
theres enough room there if the shoes moved back a little it would fall right
out ,they do rust or stick in place .