mil spec bolt headstamp question

While cleaning out a machine storage building we've discovered several
pallets of mil spec bolts and steel stop nuts. They are obviously old
aircraft military surplus, they are wrapped and boxed like only the military
would require. Most are cad plated, either gold or silver. The bolts have
head stamps of "A" and "L". The boxes seem to have mil spec identifications
other than AN, NA, or MS part numbers. Does anybody know what this head
stamp designation signifies?

I'm sure we'll just end up using them around the farm, but I'm curious as to
their specs.

Thanks
Jim