i guess it depends on the meatloaf! :-) good find!
We never had meatloaf at home so really don't know what people put in meatloaf in the 60's but certaining not what they put in it today I would think. I don't know why people feel they have to put bread or crumbs into their meatloaf or other sugars/ketchups/sauces. It's like, the recipe calls for sugar so I'll put it in without thinking. I use mushrooms, celery, onions and garlic and the loaf stays together quite well.
the original idea, i suspect, was to stretch the meat you had to feed more people. my mother's version had saltine crumbs in it. before i converted him, my husband used to make a good one with breadcrumbs. now, it's pork-rind crumbs added to his mixture of beef, pork, onions etc, with bacon draped over the top, and served with my home-made catsup or chili sauce. :-) comfort food!
Meat shrinks during cooking and releases juices, and bread crumbs could absorb it, unlike added vegetables. I found out that adding cooked then grounded meat (I usually use pressure-cooked heart)works just fine for that purpose. I add some veggies too, of course, and some eggs, raw and hardboiled.
I found that once I took the loaf out of the oven the liquid was around the shrinking meat, however, if I let it sit for a good 1/4 to 1/2 hour the liquid would be reabsorbed. Maybe I'm just an anomaly, lol
I also noticed the juices re-adsorption after some cooling-down with meat patties, you are right.